Pavements (mainly due to the non-homogeneous composition of the asphalt mixture, aggregates, underneath subgrade along with the wide variations in climatic, temperature, traffic and maintenance characteristics from one region to another) responds in a complex manner which results in surface distresses prominently fatigue cracking (load associated cracking) and rutting deformation which considerably affects the functional and structural performance of the flexible pavements, contributed mainly by high axle loading and high pavement temperature. Formation of such distresses in the pavements normally leads to the failure of these roads due to irreversible strain in the pavement. During the last few decades, the country has experienced an all round development, which has resulted into explosion in the vehicular population. The pace of road development has not been of the required order to meet the increased demand. As a result, the existing road network has become structurally inadequate to sustain the high magnitude of stresses imposed by unanticipated increase in axle loads and premature failure of the road pavements. India has to raise transportation system to a higher level both in terms of length and quality.

As construction of roads requires lot of money which can be saved considerably by appropriate engineering design principles and effective use of waste materials in the pavements. Binder modification (blending bitumen with polymers like polyethene, crumb rubber, zycosoil, sulphur, carbon black, SBS, etc.) proved fruitful and the continuing study in this line (Use of discarded waste plastics as modifier can reduce the need of bitumen by about 10%-15%, reduces the cost by (35,000-40,000)Rs per km and increases the melting point of bitumen making it suitable for application in warmer regions (Vasudevan et. al. ,2012) focuses on developing binders with better rheological and mechanical properties.

1. Professor IIT Roorkee and ex Director, NIT Delhi praveenaeron@ gmail.com
2. PG Student, Transportation Engg Group, Civil Engg Deptt, IIT Roorkee

Plastics are user friendly but not eco-friendly as they are nonbiodegradable generally, it is disposed by way of land filling or incineration of materials which are hazardous. Also, use of plastic bags in road help in many ways like easy disposal of waste, better road, prevention of pollution and so on. The better binding property of plastics in its molten state has helped in finding out a method of safe disposal of waste plastics. The coating of plastics reduces the porosity, absorption of moisture and improves soundness.

Need of the Study. Road surface with neat bitumen can cause bleeding in hot climate; may develops cracks in cold climate; possesses fewer load bearing capacity and can cause serious damages because of higher axle load in present exposure conditions due to climate, temperature, boom in traffic growth and rapid infrastructure development. So, in order to achieve longer service life and enhance bitumen pavement performance under strenuous conditions of huge growth in traffic volume; heavy axle loads; adverse varied climatic conditions(less than 00 C to 500 C); insufficient degree of maintenance; demand of bitumen more but indigenously available less; neat bitumen lose their elasticity at 700 C as their phase angle is greater than 900.

Conventional bitumen has to be modified using suitable additives [27] such as polymers, fibers, plastic, anti-stripping agent etc. There are several major industries in the country which produces a large amount of waste materials (waste plastic bags) in the form of by products, whose disposal is an alarming concern not only to regain the valuable space occupied but also to diminish the pollution and other hazards on ecology. Plastic carry bags in one form or another has penetrated into the houses of commonly in such a way that it is impractical to impose a complete ban on the use of plastic present across the nation. However by improving upon the plastic waste management system this harm can be lowered. One possible solution can be to use the waste by products effectively in the pavement layers.

So, in order to improve the properties of bituminous mixtures (healthier roads) and to reduce the negative impact of the waste materials on ecology as a whole, it seems to be practical to re-use by products from industries (through complying with the design principles) in engineering and industrial construction projects such as road pavements.

Research significance. A lot of studies are available to evaluate the effect of inclusion of plastic waste on bituminous properties. However, a comprehensive study on Indian conditions wherein a large waste is being generated annually has not been conducted.

Objective of the Study. The main objective of the study is to compare the fatigue and rutting response of conventional and waste plastic modified binders and mixtures at different stress and strain levels using LAS, MSCR, 4PBB and Wheel Rut Tester. The effect of pre-compressed waste plastic boards on fatigue and rutting responses was also being considered during the study.

Materials

1. Modifiers. Plastic fibers obtained from waste plastic carry bags and waste plastic cement carry bags were used as modifiers in this study. (Tab 1)

2. Binders. VG 10 grade bitumen was modified with waste plastic fibres though ascertaining the required specifications; properties of different binders considered in present study are tabulated below:

3. Aggregates. The aggregates used in the present study were of the following properties (Tab 3)

Experimental Investigation

The waste plastic modification can affect the rheological properties of the binders as well as bituminous mixtures such as viscosity, fatigue and rutting performances. Therefore, the present study aimed at evaluating the various performance parameters of control and waste plastic modified binders and mixtures. Firstly, control binder (VG-10) was modified with different doses of modifier. Then, the viscosity of all the binders prepared was measured at 1500 C using Rotational viscometer. Further, Superpave high temperature PG of binders was determined. The rutting performance of binders was evaluated using MSCR test parameters while that of mixes was done with wheel rut tester test procedure. Also, the fatigue performance of the binders was evaluated using LAS test parameters while for bituminous mixtures four point bending beam test procedure was followed. In middle of the study, requirements to be fulfilled for designing bituminous mixtures were checked by performing Marshall method of mix design on all the prepared samples. Lastly, plate load test was performed on the four different types of variants over a rigid CC pavement slab as a flexible overlay to rigid pavement.

1. Linear Amplitude Sweep (LAS). As per AASHTO designation: TP 101-14, it is a collaboration of test results of amplitude sweep test and frequency sweep test. Data obtained from these two tests is incorporated into VECD analysis, to determine bitumen’s resistance to damage by means of cyclic loading by introducing linearly increasing load amplitudes. During present study, a sample was prepared consistent with DSR using 8mm parallel plate geometry and 2mm gap setting. Test protocol follows two testing in successions- frequency sweep for undamaged properties and amplitude sweep for evaluating the damaged properties.

VECD analysis given by Kim et.al. (2006) was employed in order to observe the rate of damage accumulation in the binder specimens and for determining various parameters as discussed below

Determination of parameter ‘α’

Using the data for frequency sweep test results, a best fit straight line is applied on a plot of storage modulus [G′(ω)] and frequency (ω) on a log-log scale.

log G′(ω) = m(log ω) + b  (1)
using this equation, ‘α’ can be obtained as , α=1/m Determination of parameters A, B and N_f

Using the data for amplitude sweep test results, damage accumulation in the specimen at any testing time t, can be calculated as:

D_t = ∑ⁿ_i=1 [π² (C_i-1−C_i )]^α/(1+α) (t_i -t_i-1) ^1/(1+α)       (2)

D_t ≈ ∑ (π² (C_i-1-C_i ))^α/(1+α) (t_i -t_i-1) ^1/(1+α)   (3)

Where, Ct = G*(t) / G*(initial)   (4)

0= applied strain for the given data point, percent G*(t) =complex modulus at any time t, MPa It is assumed that at testing time t=0, corresponding values of C and D are 1 and 0 respectively and a relation between C_(t) and D_(t) can be established using a power law:

Where, C1 and C2 are curve coefficients which can be determined by plotting curve between (C0 -Ct ) and Dt on a log-log scale. The value of Dt at failure, Df which corresponds to reduction in initial G* at peak stress situation can be calculated as:

C_t = C₀ -C₁ (D_t ) C ^{2 (5)}       (5)

It can be linearized as,

log(C₀ -C_t )=log(C₁ )+C₂ .log(D_t )          (6)

D_f = (C₀ – C at peak stress)/ C₁ (7)

Now fatigue parameters,

A = f× (D_f)^k/k(πC₁C₂)^α (8)

B = 2α (9)

N_f = A× (_max) ^-B  (10)

Where, f is loading frequency (10 Hz), k=1+ (1- C₂) ×α and _max = maximum expected strain in the bitumen.

Significance – It is carried out in order to study the fatigue properties of the bitumen by employing cyclic loading at low temperatures. – It proves effective over the conventional procedure (Time sweep test) of finding bitumen’s fatigue properties.

2. Multiple Stress Creep and Recovery (MSCR) Test. As per AASHTO Designation D7405, sample is prepared in accordance with D7175 using 25mm parallel plate geometry with a gap of 1 mm. The sample is loaded at a constant stress for 1s and is then allowed to recover for 9s. Twenty creep and recovery cycles were run at 0.1kPa creep stress and were followed by ten creep and recovery cycles at 3.2kPa creep stress. Here the cycle of creep and recovery follows one after the other in order to evaluate out the elastic response and stress dependency of bitumen in terms of- the percent recovery and non-recoverable creep compliance (Jnr).

Creep and recovery. A specimen is subjected to a constant load for a fixed time period and is then allowed to recover at zero load for a fixed time period.

Non-recoverable creep compliance (Jnr). It is defined as the amount of residual strain left in the bitumen after application of each creep and recovery cycle divided by original stress applied to the specimen, kPa. For checking out the elastic response of binder specimens following steps were being followed.

For each of the last 10 cycles at the 0.1 kPa stress level and the 10 cycles at the 3.2 kPa stress level following observations were recorded:
₀ = initial strain value at the beginning of creep portion of each cycle
_c =strain value at the end of creep portion of each cycle (that is, after 1.0 second)
₁ =adjusted strain at the end of creep portion= _c – ₀  (11)
 _r = strain value at the end of recovery portion of each cycle (that is, after 10.0 second)

₁₀= adjusted strain at the end of creep portion= _r – ₀  (12)

Percent recovery

Percent recovery at two stress levels of 0.1 kPa and 3.2 kPa is given by:

_r (0.1, N) = 100(1- ₁₀/ ₁ ), N =11-20  (13)
 _r (3.2, N) = 100(1- ₁₀/ ₁ ), N =1-10  (14)

If some reading comes out to be negative, then a value of 0 is to be noted for that particular reading. Average percent recovery at two stress levels is given by:

R _0.1=(∑ _r (0.1, N))/10  (15)
R  _3.2=(∑ _r (3.2, N))/10  (16) 

While the percent difference in recovery between two stress levels was calculated as:

R _diff =100(1- R _3.2/ R _0.1)  (17)

Non-recoverable creep compliance (J_nr)

The value of J_nr at two stress levels of 0.1 kPa and 3.2 kPa is given by: J_nr (0.1, N) = ₁₀/0.1  (18)

But when r (0.1, N) comes to be negative, in that case J_nr (0.1, N) = ₁ /0.1  (19)

because in this situation adjusted creep strain at 1.0 second is more appropriate strain value to be used as there is no recovery.

J_nr (3.2, N) = ₁₀/3.2  (20)

But when r (3.2, N) comes to be negative, in that case J_nr (3.2, N) = ₁ /3.2  (21)

Average Jnr at two stress levels is given by: 
J_nr(0.1) =(∑ J_nr (0.1, N))/10  (22)
J _nr(3.2) =(∑ J_nr (3.2, N))/10  (23)

While the percent difference in non-recoverable creep compliance between two stress levels was calculated as:

J_{nr diff} = 100(J_nr(3.2)/ J_nr(0.1) -1)  (24)

Values of percent recovery were noted to the nearest of 0.1%, while the values of Jnr were noted to three significant figures. Significance

– It is used to identify the change in elastic response of the bitumen at two different stress levels.
– It is used to study the rutting properties of bitumen samples.
– J_nr is found to be better correlated with the rutting phenomena of pavements than the rutting factor (G*/sinδ) of PG test because in PG test system, oscillatory load to bitumen is applied at a very low strain which may not simulate better to the actual field conditions but while calculating Jnr values high levels of strains are applied.

3. Marshall Stability and Flow. About 1200 g of aggregate (of the desired gradation BC Grade 1) was taken and mixed with the different percentages of bitumen for preparing different samples. The aggregate and bitumen is heated to the required temperature for the preparation of Marshall sample. The mixture is then transferred to a pre-heated Marshall mould having a height of 63.5 mm and diameter of 101.6 mm. A mechanical hammer of standard weight is used to compact the sample. The preheated hammer was placed in position and the mix was compacted by applying 75 blows on each face of samples. Samples were prepared at four different binder content for each type of mix. Three identical samples were prepared at each binder content. The compacted samples were allowed to cool at room temperature overnight.

The extracted samples were used for the determination of the bulk specific gravity. The samples were then transferred to a pre-heated water bath having a temperature of 60 °C for 30 to 40 minutes. Test was performed on these samples following the specification laid out in ASTM D6927 and required Marshall stability and flow values were noted down. The tested sample was loosened by application of heat in the oven and is used for the determination of the theoretical maximum specific gravity (G_mm) as per ASTM D2041 using the vacuum flask method. Similarly the whole procedure is repeated at other binder contents and a series of Marshall stability, flow, G_mm, G_mb, volumetric properties values were obtained.

4. Retained Marshall Stability Test. For each type of mix six different specimens were prepared and divided into two groups, each having three specimens. Group 1 specimens were subjected to conditioning by immersing them in a water bath maintained at 60 °C for a period of 24 hours. On the other hand, specimens of group two were kept unconditioned following the normal immersing of specimens for 30 minutes at a temperature of 60 °C. All the samples were tested in a Marshall stability testing machine until failure. The average stability values for each group was calculated and the retained Marshall stability (RMS) was determined using the following equations.

Significance

– It is used to evaluate the susceptibility of the asphalt mixes to moisture which represents the durability of the mix. The higher the RMS value, lower will be its susceptibility to moisture.

5. Indirect Tensile Strength (ITS) Test. Indirect Tensile Test (ASTM D 6931-12) involves the application of load to a cylindrical specimen along its vertical diametrical plane. A nearly uniform tensile stress is developed normal to the direction of the applied load along the same vertical plane causing the specimen to fail by splitting along the vertical diameter as shown below

 Fig. 1: Load Configurations (a) and Failure of the Specimen (b) in Indirect Tensile Strength Test

 Indirect tensile strength test procedure consists of applying a load along cylindrical specimen’s diametrical axis at a fixed deformation rate of 51mm per minute until failure and determining the total vertical load at failure of the specimen. Failure is defined as the point after which there is no increase in load. The maximum load sustained by the specimen is used to calculate the indirect tensile strength with the help of the following expression. 

Indirect tensile strength (MPa) = 2P/πDH  (26)

Where, P -the load till failure of the specimen (newtons), D -average diameter of the Marshall specimen (mm) and H -average height of the Marshall specimen (mm).

A high value of indirect tensile strength is an indication of higher resistance to low temperature cracking and the capability of mix to withstand larger tensile strains prior to cracking.

Tensile strength ratio (TSR) is the average indirect tensile strength of the conditioned specimens expressed as percentage of the average indirect tensile strength of unconditioned specimens. Conditioning was done by keeping the specimens in water maintained at 60 °C for 24 h and by curing at 25 °C for 2 h before commencing the test. Mixes for which the minimum specification criteria of 80% TSR was not satisfied, anti-stripping agent should be used to protect them from being vulnerable to moisture effects.

Significance

– It is useful in assessing the tensile properties of the asphalt mixes which can be correlated with the cracking of the pavement.
– It is also significant to evaluate the sensitivity of the mixture to moisture damage.

6. Wheel Rut Testing. As per the rutting testing protocol of AASHTO T-324, a small loaded wheel is rolled repeatedly across a prepared HMA specimen to measure parameters like rut depth, dynamic stability, etc. The test can be done both in air and water control modes. In this study, air control mode was used to simulate the effect of air temperature on the pavement in terms of rut displacement. As the height of beam was fixed, the weight of the mixture required to achieve the target air void was pre-calculated. The aggregates and bitumen were mixed at the required mixing temperature and were placed in the pre-heated mould. A compression testing machine was used for applying load till the desired height was achieved. After compaction the specimen was allowed to cool for 24 hours. The sample was extracted from the mould and the air void content was measured using the saturated surface-dry procedure (AASHTO T166). As the height of the sample is fixed, it might happen that due to different orientation of aggregate particles within the mix for different specimens slight variation in the fixed air void content of 4% may result. So an allowance of ±0.4% was given to the required air void content. The testing protocol mentioned below was adopted for conducting the wheel rut tester test.

Significance – It is used to measure the pavement quality in respect of its susceptibility to rutting distress.
– It also evaluates the moisture susceptibility effects in flexible pavements under water control mode during its operation.

7. Four Point Bending Beam Test (4PBBT). The flexural fatigue testing protocol of AASHTO T321-2003 requires dimensions which are 380 ± 6 mm in length, 50 ± 6 in height, and 63 ± 6 mm in width. All the specimens were prepared to achieve a target air void content of 4% by weight of the total mix through similar procedure as was applicable for rutting specimens. The testing protocol mentioned below was adopted for conducting the four point beam bending (4PBB) test.

Significance – It is used to evaluate the performance of the bituminous mixtures for their susceptibility to load associated cracking in low temperature conditions.

8. Plate Load Test. Plate load test is used to evaluate the support capability of subgrade, base and in some cases complete pavement. It involves measurement of modulus of subgrade reaction for in situ material through analysing a load settlement curve. Plate bearing assembly comprises of a bearing plate which is pressed using a hydraulic jack onto the surface to be evaluated and surface deflections are being noted down corresponding to the increased load values from the jack.

The modulus of subgrade reaction is determined by- 

k = P/∆ (27)

Where,
k, modulus of subgrade reaction p, applied pressure ∆, measured deflection

Significance – As per AASHTO T 222, plate bearing procedure is useful for evaluation and design of airport and flexible pavements.

9. Proportioning of Bituminous Mixtures Ingredients. Rothfutch procedure was adopted for blending aggregates used in bituminous mixtures whose results are tabulated below-

Results and Analysis

1. Multiple Stress Creep and Recovery Test Results. The results obtained for binder specimens using MSCR test procedures, compared at different test conditions are tabulated below – (Table 8)

Since, % recovery is an important consideration while evaluating the performance of binders under high temperature rutting deformation criteria.
Higher is the % recovery better will be the resistance of binder to the rutting susceptibility. At lower creep stress level of 0.1 kPa for temperatures of 400 C and 700 C, values for recovery % are
more-less same but at 500 C and 600 C there is an increase in the values by about 1.44 times and 2.18 timesrespectively. At higher creep stress level of 3.2 kPa, modified bitumen showed a
throughout improvement across the considered temperature range (Fig-2).

Since, lower values for non-recoverable creep compliance Jnr are proven favorable while checking the rutting deformation resistance of binders under high temperature climatic regions. So, by modifying base bitumen with waste plastic fibres the values of Jnr at creep stress of 0.1 kPa get reduced approximately to 2.27 times, 4.69 times, 5.18 times and 3.5 times the corresponding values of unmodified bitumen at 400 C, 50⁰, C, 60⁰, C, and 70⁰, C respectively (Fig-3.While, at higher creep stress of 3.2 kPa, the reduction in values of Jnr achieved were 3 times, 3.8 times, 3.95 times and 3 times at temperatures of 40⁰C, 50⁰C, 60⁰C and 70⁰C respectively. It proves the suitability of waste plastic modified binders under warmer conditions for laying flexible pavements.

2. Linear Amplitude Sweep Test Results. The results obtained for binder specimens under study using LAS test procedures at varied temperatures are tabulated below (Table 9):

At lower strain levels of 2.5% when the impact of vehicles is not so significant regarding tensile strain at the bottom of top layer of flexible pavements, the improvements obtained in terms of fatigue

life of pavements by modifying the bitumen were better by 2.1times, 2.3 times and 1.8 times at 100 C, 200 C and 300 C respectively (Fig-4). Under higher strain conditions of the level of 5 %, modifier showed improvement approximately of the order of 1.46 times, 1.87 times and 1.37 times the base bitumen performance at 100 C, 200 C and 300 C respectively.

3. Four Point Bending Beam Test Results. At low temperature, cracking performance of bituminous mixtures was found to be 2.1 times and 7.4 times (compared to the performance of control mix) with the modification via dry process of mixing and introducing waste plastic boards respectively(Fig-5). Whereas mixing of ingredients via wet process shows lesser fatigue life cycles than that for control mix, which may be attributed to the formation of more organized network structure of the binder with the modification .

4. Wheel Rut Tester Test Results. Under high temperature condition the rutting susceptibility increases which results in poor resistance of bituminous mixtures to the rutting deformation. In the present study, when compared with the results of control mix, the bituminous mixtures prepared with modifications in one way or other showed an improvement of around 1.27 times using wet process of modification. On the other hand, with the use of dry process of modification or waste plastic boards as modifiers to the base condition, the results were on the negative side because of the poor interlinking between the various ingredients of the bituminous mixtures.

5. Moisture Susceptibility Tests Results. Since, the durability of the mix design is an important consideration while looking at the susceptibility of mixes to moisture and climatic conditions. The results obtained (Fig-7) after conducting the standard test procedure of Retained Marshall Stability and Indirect Tensile Strength for moisture susceptibility were found satisfying the minimum criteria for the same. Dry procedure of mixing the waste plastic shredded fibres reflects the resistance against the moisture better to wet procedure of mixing which may be attributed to the formation of plastic coating over the aggregates resulting in the reduction in the penetration of water which in turn increasing the service life of pavements.

6. Plate Load Test Results. The results obtained for bituminous mixtures after performing plate load assembly test procedure, for checking out the deflection regarding ability of storing the strain energy in the respective mixtures are tabulated below (Table 10-14.)

Since, area under the load deflection curve represents the estimation of energy absorbing capacity or toughness of the mix materials which in other words meant for the improved performance regarding resistance of the mix materials to fatigue. Dry procedure of mixing the various ingredients of the bituminous mixtures was found to give best results (Table 14) in this context attributed to the increased load carrying capacity of ingredient aggregates and to flexibility imparted by the way of modification.

The structural evaluation of pavements can be looked in terms of the support stability of the underlying pavement layers through modulus of subgrade reaction, k values. The use of binders modified by waste plastic fibres showed higher results (Table 14) as compared to control mix but the mix with waste plastic boards wherein the deformation was highest with a little load to bear provided least results.

Conclusions

Based upon the study performed the following conclusions were drawn
1). Addition of waste plastic shredded fibres at optimum content of 4% by weight of bitumen to the base binder has improved its conventional properties namely – penetration value, softening point and viscosity.
2). Modified binder prepared using waste plastic fibres was found suitable for its application in warmer areas as shown by PG test results in terms of rutting factor (G*/sinδ) and MSCR test results in terms of non recoverable creep compliance (Jnr).
3). With the modification, improvement in conventional and rheological parameters was significant but within the modification 4% CB as modifier was found superior to 4% CCB.
4). Wet procedure of mixing the waste plastic shredded fibres for preparing the bituminous mixtures resulted in lowest fatigue life as shown by 4PBB test results but was found the best mix regarding the rutting resistance shown by Wheel Rut Tester test results.
5). Dry procedure of mixing the waste plastic shredded fibres for preparing the bituminous mixtures reflected best results regarding the performance of mixtures for durability aspects as shown by RMS and TSR test procedures.
6). With the modification, improvement was observed in the support capability (modulus of subgrade reaction, k value) of pavement layer as observed by the Plate Load test results.
7). Waste plastic boards as a way of modifying the bituminous mixtures were found better in fatigue performance and shear cracking considering the results obtained through 4PBB and ITS test procedures, but were not found advantageous regarding rutting performance as depicted by the results obtained from Wheel rut tester and Plate load test procedures.

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35. MoRTH, 2013. Specifications for roads and bridge works. Indian Roads Congress, New Delhi, India. 36. Nuñez, J.Y.M., Domingos, M.D.I. and Faxina, A.L., 2014. Susceptibility of lowdensity polyethylene and polyphosphoric acid-modified asphalt binders to rutting and fatigue cracking. Construction and Building Materials, 73, pp.509-514.
37. Panda, M. and Mazumdar, M., 2002. Utilization of reclaimed polyethylene in bituminous paving mixes. Journal of Materials in Civil Engineering, 14(6), pp.527-530. 38. Pérez-Lepe, A., Martínez-Boza, F.J. and Gallegos, C., 2005. Influence of polymer concentration on the microstructure and rheological properties of high-density polyethylene (HDPE)-modified bitumen. Energy & Fuels, 19(3), pp.1148-1152. 39. Polacco, G., Berlincioni, S., Biondi, D., Stastna, J. and Zanzotto, L., 2005. Asphalt modification with different polyethylene-based polymers. European Polymer Journal, 41(12), pp.2831-2844.
40. Punith, V.S. and Veeraragavan, A., 2007. Behavior of asphalt concrete mixtures with reclaimed polyethylene as additive.  Journal of Materials in Civil Engineering, 19(6), pp.500-507.
41. Qisen, W.H.L.X.Z., Yu, C. and Xue-lian, L., 2009. Rutting in asphalt pavement under heavy load and high temperature [J].  China Civil Engineering Journal, 5, pp.10-26.
42. Rokade, S., 2012. Use of waste plastic and waste rubber tyres in flexible highway pavements. International Conference on Future Environment and Energy, IPCBEE, 21-23 November, Sicily (Vol. 28, pp.247-283).
43. Saboo, N., 2015. Strength characteristics of polymer modified asphalt binders and mixes. Ph.d. Thesis, Transportation Engineering Group, Department of Civil Engineering,IIT Roorkee, India, pp.269-293.
44. Saboo, N. and Kumar, P., 2015. A study on creep and recovery behavior of asphalt binders. Construction and Building Materials, 96, pp.632-640.
45. Soenen, H., De Visscher, J., Tanghe, T., Vanelstraete, A. and Redelius, P., 2006. Selection of binder performance indicators for asphalt rutting based on triaxial and wheel tracking tests. J Assoc Asphalt Pavement, 75, pp.165-201.
46. Vasudevan, R., Sekar, A.R.C., Sundarakannan, B. and Velkennedy, R., 2012. A technique to dispose waste plastics in an ecofriendly way–Application in construction of flexible pavements.  Construction and Building Materials, 28(1), pp.311-320.

Paul Guinard
Director of Civil Engineering
SOPREMA

As renovations are increasing on civil Engineering structures in most of the countries, the re-profiling of surface bridge decks is becoming common but this is not without risk, especially, for the implementation of the successive waterproofing layer and wearing courses. New PMMA resin-based products offer a quick and effective solution that fulfills both the roles of re-profiling and also as pore filler primer for waterproofing by liquid PMMA resin or by bitumen prefabricated sheets.

Current Re-Profiling Techniques

In order to ensure the safety and comfort of users, infrastructure owners must carry out regular renovation campaigns for bridge structures. In particular, the bridges and structures of major motorway projects built over 30 years ago must be regularly monitored. The work for repairs needs the traffic to be stopped during the intervention period. The duration of this stoppage depends not only on the extent of the work to be carried out but also on the techniques used. In general, as the “time” factor is essential. In particular, for re-profiling the surface of the concrete of the deck after wearing course planer, solutions to limit traffic closure are preferred.

Re-Profiling with PMMA Resin

During the renovations of the structure, the wearing course in asphalt and the existing waterproofing layers are planned in such a way so as to find the concrete substrate for control, to be able to repair it and/or strengthen it and then to rebuild the waterproofing layers and the wearing course layers. Unlike new structures on which the surface of the concrete is regular and smooth; old supports, very rarely meet the actual specifications and requirements for the implementation of the modern waterproofing systems: planimetry, cohesion, roughness.

This can be explained by multiple reasons:
– The concretes implemented in those years were not as good quality as those of today
– The action of the planer alters the surface quite strongly and makes an irregular surface
– The old structures were often designed with no slope, which does not allow water runoff and is nowadays strongly discouraged

As a result, re-profiling and a new surface preparation are often necessary

There are currently three main techniques for surfacing support:

– Pouring a hydraulic mortar thin slab (so-called white re-profiling)
– Adding an asphalt layer (so-called black re-profiling)
– Using of charged resins

The first technique should be used when the concrete is badly damaged and requires extensive repairs with possibly reinforcement. It is suitable to use this solution on the entire surface in order to avoid side effects (small steps, peeling, punctual concrete removing). It can also be used for filling spot holes but a specific treatment of the contours is then necessary. It should be noted that, in the implementation of the superior waterproofing layers, a minimum drying period of 14 days will be required in order to limit the concrete water content.

The black re-profiling is now often used for projects requiring rapid implementation. It consists of placing a 2 to a few centimeters thick layer of concrete asphalt on the entire bridge deck. This operation requires heavy machines but presents the advantage to be carried out at high speed, so it is particularly interesting for large works. For small works, it is often expensive and other solutions are preferred. It should be noted that this technique creates an increase in weight on the structure, weight that must be integrate in the calculation of the structure resistance. As far as waterproofing is concerned, this solution has advantages and disadvantages. The first advantage is to have a bitumen made support on which the bituminous membrane will be easily welded with a very good level of adhesion. The second advantage is that, because the concrete asphalt is porous, the pressure rises of the air contained in the substrate are diffused and the risk of blistering of the membrane is thus greatly reduced. But this advantage can also become a risk.

If, by accident during the work phases or during exploitation, the bituminous membrane is punctually damaged, the water that will enter by this defect will be able to circulate in the under-asphalt layer over the entire structure limitlessly and without any way of detecting the place of leakage. In many cases, the recovery will then have to be the total surface. The re-profiling with charged resin technique is, for now, less used around the world because the products offered are mainly epoxy-based and the conditions of their use are quite difficult to meet (especially the temperature). In addition, epoxy and epoxide mortars are, by nature, quite rigid. This feature allows for good resistance to compression but low flexibility (not to forget that a bridge deck is mainly used in bending). Thus, it is not advisable to set up these products on large thicknesses and it is not suitable to re-profile large surface (only local repairs of holes are possible).

Bridge Deck Before Re-Profiling

In order to overcome the problems faced by the waterproofing applicators with the quality of the substrates after planers, SOPREMA, a French specialist in waterproofing and insulation, conducted research, carried out numerous tests with different types of products and finally developed an innovative solution that meets most of the requirements of the product needed for a perfect re-profiling: speed, regularity, flexibility, compatibility with bituminous membranes and liquid waterproofing. This solution is based on the use of PMMA resins

PMMA Resin

Methyl Poly Methacrylate or PMMA is a thermoplastic polymer initially known for its use in the development of unbreakable windows (the best-known brand is Plexiglas©). It is also used in paints, waterproofing resins, dental products and lubricants. Thanks to its properties, including its transparency, mechanical resistance and resistance to climatic effects (UV, water presence and temperature changes); it is now used in many industries.

For its application on site, the resin is proposed in a two-component form: resin (liquid) and catalyst (powder). It will be charged with silica added to the mixture in order to increase the volume and to reduce the cost of the final mix while maintaining a good fluidity for its easy application.

Implementation On Site

Prior to application, the substrate must be cleaned from all non-cohesive parts (no oil, no dust) and be dry so that the product can bond properly to it. The application of re-profiling must be implemented with a substrate constant or decreasing temperature (usually in the early morning or in the evening) in order to avoid blistering in the resin. The application under sun is prohibited.

The resin-silica mixture is made cold directly on the site by using a mixer with a ratio of 1/1 in weight. The silica is placed in the resin pot (maximum 10 kg in order to be manually installed) and mixed. Once the mixture is homogeneous, the catalyst is integrated and mixed for about a minute. The amount of catalyst to be incorporated into the mixture depends on the outside temperature:

Temperature between 20°C (68°F) and 35°C (95°F): 1 x 100 g pack for 5 kg of resin

Temperature between 3°C (35°F) and 20°C (68°F): 2 x 100 g packs for 5 kg of resin

Mixing of Resin, Silica and Catalyst

Apart from the minimum and maximum quantity, the exact amount of catalyst does not influence the quality of the result but mainly changes the reaction speed of the resin and thus its possible application time. The introduction of the catalyst causes the start of the reaction for the entire mixture. The mixture is easily applied on the deck by achieving a “zero pull” with the raclette in order to fill all defaults and holes. The resin must be spread out before hardening. No sand dusting is required on the resin layer The amount of re-profiling mixture to be implemented is generally between 1 kg (0.5 kg of resin and 0.5 kg of silica) for a low-damaged support and 2.5 kg for a medium with large grooves.To fill a local hole, there is no thickness limit (from a film to about ten centimeters) but the thickness needs to be limited (1 to 2 mm maximum) on large areas to reduce the tension on the substrate. The reaction is exothermic and gives off a characteristic odor without specific toxicity.

Once the resin has reacted, it presents itself as a pale-yellow hard layer. Site traffic is possible directly on the resin about fifteen minutes after implementation. Because the resin is not sensitive to UV (a slight change in colour may still take place), the resin can be left exposed for several days.

Where necessary, the welding of the bituminous membrane (manually or using automatic laying machines) is possible two hours after the installation of the resin without adding any tack coat. High temperature resistance allows its use both under bituminous membranes and under asphalt-based systems.

Where requested, the application of liquid waterproofing (PMMA resin) is possible 30 minutes after implementation.

It is advisable to entrust the resin re-profiling works to the company in charge of the waterproofing application. The use of two-component resins requires know-how and the selected waterproofing systems (liquid or bituminous membranes) must be compatible. It should be noted that the use of PMMA resin for re-profiling a substrate can be also considered as pore filler (strongly limiting the risk of blistering) in the use of bituminous waterproofing membranes.

Implementation

Bituminous Membrane Welding by Machine

The Interests Of This Technique

This innovative re-profiling solution in PMMA resins offers many advantages over traditional techniques:

– The speed of the PMMA reaction saves valuable time while requiring neither heavy machine nor specific contract as it is usually implemented by the waterproofing applicator. Even on local areas treated with a high thickness, the support will be circulating in a few minutes and the waterproofing products can be implemented two hours after application.

– The temperature conditions possible for the implementation of this product (between 3°C (35°F) and 40°C (100°F) allows work to be carried out in any season (the only reservations are that the substrate is not frozen and that it does not rain)

– The PMMA resin allows the result of a very puncture resistant re-profiling while having a good flexibility limiting its surface cracking. It should be noted that there is no edge effect as the product can be placed even with very limited thicknesses. The product can therefore be used by area.

– The SOPREMA resins are compatible to direct welding of the bituminous membranes and acts as a pore filler. Welding does not require any additional tack coat.

This solution has been implemented on several projects carried out in from 2017 in Europe with excellent results promising a bright future for this technique.

SOPREMA has built two production units specific to PMMA resins in order to answer to all requests and to maintain a high level of quality on these products.

Product information (SOPREMA manufacturing): PMMA resin:
ALSAN REKU P70 in 25kg buckets Catalyst:
ALSAN CAT in 100g packs Silica: ALSAN Fine Silica in 25 kg bags
Products available for direct sale

An effective waterproofing solution ensures durability of the structure by controlling water seepages. Eco-friendly and high-performance proofing solutions are essential for multi-level applications in a building, terrace water proofing is particularly important and is considered a priority as the roof is always exposed to harsh climatic conditions and weather changes.

Waterproofing of flat terraces are extremely challenging as the water cannot run off the structure quickly, and will move slowly or pool above the surface, leading to leakages.

A wide range of products are available in the market, of different qualities ranging from basic ones to premium and advanced materials. Each of them catered to the specific requirement.

Alongside water proofing, managing thermal comfort of the occupants is to be considered keeping in mind the well-being of the people and also to cut down on energy requirements.

Constructing energy efficient buildings will show a significant contribution to protecting the environment. It ensures reduction in the power bills, contributing to saving of fossil fuels. High levels of comfort are obtained through the effective utilization of sunlight, ventilation, and other modern methods of construction.

Thermal comfor t can be provided to the occupants, at a diminished levels of power usage by adopting strategic planning of building designs, and effective use of heat insulation materials in the construction.

Why Is Thermal Insulation Required For Buildings?

In countries with extreme climatic conditions more than 65% of the energy consumption goes on air conditioning to maintain soothing indoor temperatures. This poses a great challenge to architects and designers to conduct major analytical studies, to make maximum utilization of natural resources like lighting, ventilation, along performance oriented thermal insulation materials limiting of the U-value for roofs and external walls in the buildings. Use of high-quality insulation materials, has proved to be result giving in controlling the heat transfer through the walls. Premium quality insulation material reduces the rate of heat transfer from outside to inside during hot summer and the reverse during cold winters.

The quantum of heat transfer through roofs and walls ranges between 60-70%. This heat shall be removed by air-conditioning. Therefore, the use of insulation materials for roofs and walls is very essential for energy conservation as it helps in:

1. Reducing the energy consumption required for cooling and heating.
2. Reducing the capacity of air-conditioning equipment and hence reducing capital cost.
3. Reducing thermal stresses (thermal expansion and contraction with temperature changes).
4. Maintaining comfortable indoor thermal environment.

With the increasing emphasis on sustainability and sturdiness along with the introduction of recent ECBC codes, the concept of terrace waterproofing together with thermal insulation is becoming a replacement trend, especially in commercial buildings and high-end residential buildings. Although it may require higher initial costs, but overall life cycle costs are much lower because the payback is achieved within few years (generally 5-7 years).

Key Selection Criteria For A Good Thermal Insulation Material For Roofs: – Low Thermal Conductivity – Dimensional Stability – Higher Compressive Strength – Negligible Water Absorption and Low Vapour Permeability – Fire Resistance

Recent Trends In Roof Waterproofing

Roof Waterproofing Along With Thermal Insulation

A high-performance roofing system is achieved by combining waterproofing alongside thermal insulation. It includes a highly impermeable and sturdy waterproofing membrane that guards against extreme climatic conditions, irregular temperature variations, rain, and suitable thermal insulation material.

Generally, insulating materials like spray applied PUF insulation, XPS, or EPS insulation boards are applied in a controlled thickness (as recommended by the consultants) on the well-prepared, clean substrate followed by liquid applied waterproofing membrane like spray-applied Polyurethane or Polyurea membrane or sheet membrane-like TPO or vice-versa and with or without protection screed. A typical system that is being employed at a prestigious project site, is shown

Green Roof Solutions

Garden roof systems are the specialized roofing solutions that are designed for supporting roof gardening. Green roofs provide a variety of benefits in an urban context starting with giving an aesthetic appeal to the unused roof. The plants and soil protect the roofing membrane from being exposed to the harmful ultraviolet rays, extreme climatic conditions and physical damage, thereby increasing the durability and life span of the roof and roofing material. Green roofs contribute to lowering the greenhouse gas emissions, by means of direct shading of the roof, evapotranspiration and improved insulation values.

A typical Green Roof System Includes The Following: – Durable Waterproof Membrane (ECMACOAT FLEX PU 40 or ECMACOAT FLEX PUR 10) – Root Barrier – Drainage Layer – Filtration Media (Geo-textile Mat) – Growing Media or Soil (50-100mm in depth) – Vegetation layer (Low growing, stress tolerant alpine and herb species) The components act together to provide a suitable environment that supports plant growth while not compromising the waterproofing function of the roofing membrane.

Cool Roof Solutions

Dark-colored roofs absorb the Sun’s energy and get hotter as the day progresses. The roof surface can become superheated up to 80°C on a 35°C normal day, and therefore, the temperature of rooms below becomes unbearable leading to the increase in air-conditioning costs. Hot buildings also increase the Urban Heat Island effect.

The best method is to stop the roof space from heating up in the first place by reflecting heat away from the roof surface. A cool roof is a one that has been designed to reflect more sunlight and absorb less heat than a typical roof. Cool roofs are often made from a highly reflective sort of paint or a sheet membrane.

ECMAGUARD THERMOCOAT is a cool roof coating with high SRI (roof’s ability to reject solar heat) and low thermal conductivity, is capable of reflecting large portion of ultraviolet, infrared and visible light and offering a list of benefits to the building occupants as mentioned below: – Reduces indoor temperature by 5-10oC (improved thermal comfort) – Reduces roof surface temperature by 15-400 C – Reduces air-conditioning costs – Helps reduce heat islands – Can be applied over a variety of roof surfaces

High Performance Waterproofing Although, multiple choices are available to the building owners and designers fitting into their technical requirements and budgets. Some common solutions are Cementitious coatings, liquid applied Acrylic coatings, Polyurethane and Polyurea membranes, Bituminous sheet membranes, TPO membranes, etc. but liquid applied pure Polyurethane and Polyurea membranes from ECMAS have become increasingly popular thanks to their long-term heavy-duty performance and optimal costs. ECMAS offers a multiple choice of high-performance PU and Polyurea membrane which are ideal for waterproofing huge terraces, green roofs, and podiums.

Non- exposure grade pure Polyurethane membrane (ECMACOAT FLEX PU 40); Exposure and trafficable grade pure Polyurethane membrane (ECMACOAT FLEX PU 60); Hybrid Polyurea membranes (ECMACOAT FLEX PUR 10 and PUR 20) are popular high-performance, liquid applied waterproofing solutions offered by ECMAS.

Insulation Materials: Roofs are often insulated either over the deck or under the deck. Generally, over-deck insulation is preferred to avoid the absorption and retention of warmth by the concrete surfaces. Commonly used roof insulation materials include Expanded Polystyrene boards, Extruded Polystyrene boards, Spray applied PUF Insulation, Foam Concrete, Exposure grade liquid membranes with high SRI; etc. ECMAS is a leading player offering high-performance thermal insulation products like ECMAFLEX PUF 40 which is a two-component, polyurethane resin (PUR) based, seamless, fully bonded, closed-cell rigid foam to be applied with a specially designed spraying machine. It provides high-performance thermal insulation for terraces, green roofs, walls, etc.

ECMASHIELD TPO is the eco-friendly sheet membrane system, a perfect solution for both heat shielding and waterproofing roofs.

Thanks to its high SRI values with high emissivity — it reflects over 90% of the sun’s heat, thus insulating the roof below. This exceptionally durable and versatile membrane does not allow water to percolate below, thereby waterproofing at the same time. ECMASHIELD TPO membrane is efficient, eco-friendly, and straightforward to put in solution for many projects (old or new construction, terraces of residential, commercial, or industrial buildings).

Conclusion

The advancements in construction technology, have led to a growing trend for high-rise constructions. These constructions look out for modern methods for increasing sustainability and energy saving options. Demand for high performance waterproofing and insulation systems has grown exponentially. Green roof and cool roof solutions are the talk of the town today providing quantitative benefits to the building owners and better comfort levels to the occupants. This is accelerating the demand for better insulation products such as spray applied PUF insulation, XPS boards, high albedo solar reflective coatings, high performance waterproofing solutions to support the latest trends.

Samir Surlaker
Director
Assess Build Chem Private Limited

Sunny Surlaker
Head Technical Services
Assess Build Chem Private Limited

The fundamental certainty of concrete is that it will crack.

Concrete is known to have the ability to sustain high compressive loads. The ability of concrete to sustain tensile and flexural loads on the other hand is very limited due to its brittle nature. The concrete is therefore prone to cracking when the tensile stresses in the concrete exceed its tensile strength. When compared, the tensile strength of concrete is barely 1/10th the compressive strength of concrete. That is the reason, why concrete is reinforced with steel.

Concrete may crack due to many reasons, viz., improper mix design, insufficient curing, improper joint design, overloading, shrinkage and many other factors. These may occur due to errors in the construction stage (improper design, improper mix design, improper workmanship) or due to loading after construction (mechanical overloading, accident, fire, thermal changes, chemical attack or biological attack). Some of the types of cracks and/or their causes are shown in Figure 1.

In practice, we cannot eliminate cracks completely, but with proper mix design, production, placing, compaction and curing practices, we can limit the extent of cracking to a degree where it will not adversely affect the structure. For durability purposes international codes recommend limiting the crack widths in concrete to:

• ≤ 4 mm crack widths for interior structural elements
• ≤ 3 mm crack widths for external structural elements exposed to weather
• ≤ 2 mm crack widths for special structural elements exposed to weather or special loads
• ≤ 1 mm crack widths for structural components where waterproof concrete is being used, e.g. in basements, tunnel sections, etc.

The problem with cracks is that they are both a symptom and a cause. General perception of cracks is that they are unsightly, and observers feel that the element that has cracked has failed. In the case of walls, if a crack is not structural, is not too wide and is not leaking water, it may be considered acceptable.

Cracks may affect RCC elements in three fundamental ways:

1. It may affect/reduce load carrying capacity as loads around the crack are redistributed
2. It surely affects the durability of the structural element by allowing water, chlorides and other aggressive elements easy access to the reinforcement

Fig. 1: Types of Cracks

3. It’s a precursor to loss of serviceability of the structure as corrosion begins from cracks, propagates and leads to further cracking Cracks are also a fundamental problem in waterproofing as these are the primary avenues for water to enter the living space. Therefore, for both new structures as well as remedial waterproofing, repair of cracks becomes very important to seal water ingress pathways. The repair of cracks alone cannot guarantee the structural stability or durability of concrete and therefore, if necessary, should be complimented with other treatments as per the established practices of civil engineering.

Understanding Cracks

Before we can start to treat cracks, we need to understand them. Solutions to treat cracks are not universal. They are based on the characteristics of the cracks themselves. Cracks (shown in Figure 2) can be characterized based on:

Crack Depth: Near Surface or Deep Cracks Crack Width: Crack Tip Width, Crack Width at Surface Crack Movement: Moving or Static Crack Wetness: Dry, Damp, Wet or Pressurized Flow through

Fig. 2: Characteristics of Cracks to be Evaluated

Prior to selection of a material and method to remediate a crack or void, the characteristics of the defect need to be clearly assessed. Assessing these properties will help us in selecting the correct material and in turn determine the success of the crack repair. Injection is the first step of rehabilitation both when structural distress is encountered as well as when leakages are detected, and durability of the RCC Element/Structure is compromised. The injection technique is often the only viable solution in order to repair/waterproof damaged structures and thus avoid any further ensuing consequential damage. Table 1 shows various reasons for Injection.

Summary Of Remedial Measures

Some of the remedial measures based on the characteristics seen above can be summarized in the schematics and sections below.

1.      Solutions Based On Crack Depth

A summary of these methods is shown in Figure 3. Near Surface Cracks (up to 5 mm) can be repaired by simply coating them with a crack bridging coating, by impregnating the crack with a low viscosity resin grout or by cutting a groove along the crack, filling it with a fine polymer modified mortar and overcoating it with a crack bridging coating.

Fig. 3: Summary of Crack Treatment Methods Based on Crack Depth

2.      Solutions Based On Crack Width The injection grout material and methods also need to be selected on the basis of crack width. The width of the crack will dictate the viscosity and particle size of the injection grout. The types of materials that can be used for different crack widths are shown in Figure 4.

Fig. 4: Material Selection for Grouting Based on Crack Width

Generally, as a rule of thumb, mineral slurries (cementitious injection grouts) are most suitable for crack widths or voids > 1.5 mm. Hence in many of the cases of waterproofing where cement grouting is used, it is unable to fill the finer cracks in the concrete and the leakage continues. Hence, for Crack Widths < 1.5 mm it is recommended to inject / grout them using a resin [Epoxy or Polyurethane].

3.      Solutions Based On Crack Movement

The movement characteristics of a crack needs to be carefully evaluated before it is treated. In more cases than not including for structures such as terraces, podiums, which are slightly dynamic due to thermal or traffic variations. In these cases, when cracks are treated with a rigid material such as Cement, Epoxy, Methacrylate or even PU Foam, the rigid nature of these systems are unable to cope with the minute movements in the concrete elements and the system gives way, starting the leakage problem again. The selection of material systems based on crack movement are shown in Figure 5.

Fig. 5: Material Selection Based on Crack EP

4.      Solutions Based On Crack Wetness

Wetness of the crack has quite an impact on material chosen. For e.g. the materials used for repairs or strengthening such as cementitious grouts and epoxies can be applied in dry or damp conditions, but not when a crack is leaking water. In those cases, the only system that can work is an elastic methacrylate gel or polyurethanes. The table based a German Standard for Repair, 2017 is shown in Figure 6. This table guides the selection of various crack filling materials based on the wetness of the crack.

Going by these four considerations, the material and method selection becomes very important in treatment of cracks. Most often than not, these guidelines are not followed in practice and the crack treatment remains ineffective, being referred to as “failed waterproofing”.

The Materials

Assessing cracks for the properties discussed previously will help us in selecting the correct material and in turn determine the success of the crack repair. Internationally and in India at the moment, the following types of filler materials are being used for crack/void filling:

• Epoxy resin (EP)
• Polyurethane (PU)
• Cement slurry (FC)
• Micro fine/fine cement suspension (MFC)
• Injection Hydrogels Based on Methacrylate/ Polyurethane Resins [AG]

There are two different ways to fill the filling materials into the cracks and voids of a structural component:

• Injection: Filling of cracks and voids under pressure through packers (filler plugs)
• Impregnation: Filling of cracks without pressure (by penetration, gravity and atmospheric pressure)

Fig. 6: Guidelines on Selection of Materials Based on Crack Wetness

In Brief, Table 1 below gives an idea of the type of Injection materials available and the conditions these materials can be used under.

The Process Of Injection

After completion of diagnosis and selection of materials for injection the work of injection passes through following stages:

1. Preparation of the crack
2. Location of points for injection
3. Surface sealing of cracks
4. Injection of resin proper
5. Removal of packers and plugging
6. Removal of sealing material
7. Final surface treatment after injection resin/grout hardens

Injection Machinery And Appurtenances

1.      Machinery

The Injection process comprises of the mixing device, the injection device, packers (filler plugs), possibly an injection hose and insulation, if necessary. The manufacturer generally provides the methodology for the work with the approved system components. The equipment required for crack injection can range from a simple bucket with an outlet to most sophisticated pneumatically compressed machines capable of producing about 500 bar pressure. Other variants are available with hand-controlled nozzles with a mixing assembly to mix the two components at the point of injection. Modern sophisticated machineries are designed to provide better working pressures, better nozzle / packer combinations and to take care of pot life considerations.

Modern Injection Machinery for injection of cementitious materials, a one component injection pump and a two- component injection pump are shown in Figure 7.

The injection method should be clearly specified prior to the commencement of the work and should be supervised to conform to the specifications. After the injection resin or grout has hardened and after the removal of the nipples, the surface sealing material, which is normally quick setting cementitious system or resin should be scrapped off completely and the surface should be prepared for further cosmetic or strengthening treatment.

2.      Selection Of Packers For Injection

Packers or Nipple Systems are the link between the structure and face of the crack and the injection nozzle. Packers must be of adequate size to guarantee the flow of injection resin to the desired place with or without being displaced or de-bonded due to injection pressure or rebounds. The critical selection depends upon the access to crack, quality of surface, surface condition as well as pressures used in injection process. Figure 8 shows different type of commonly used packers for Injection Grouting.

 Fig. 7: Modern Injection Machinery

Fig. 8: Commonly Used Packers for Injection Grouting

There are normally three types of Packers used under general conditions:

1. Adhesion Packers: For the injection of dry cracks, cavities and substrates with Epoxy and Polyurethane resins where surface conditions are suitable and
2. Drill or Bore Injection Packers: for the injection of dry, moist and water bearing (pressurized and non-pressurized) cracks, cavities and substrates with Epoxy, Acrylic and Polyurethane resins
3. Hammer Packers: for the injection of cement injections and acrylic The main differences are valve openings, dimensions and pressures.

Conclusions

In conclusion, modern injection technology coupled with proper equipment can solve almost all types of waterproofing problems thereby providing economical solution in comparison to removal and replacement of older waterproofing systems. The specifications should be very clear and unambiguous. The specifications should at least cover points like material, viscosity, techniques to be adopted, the equipment to be employed, type of nozzles and spacing, pressure to be applied etc. The repair of cracks is a part of waterproofing and repairs of damaged and distressed structures and cannot replace other remedial measures adopted for successful waterproofing.

Ishita Manjrekar
Technical Director
Sunanda Global

Sourabh Manjrekar
Director – Operations
Sunanda Global

Non-prestressed reinforced concrete liquid containment structures—in particular, non-circular tanks, often exhibit vertical and diagonal cracks that are aesthetically objectionable. More importantly, cracks could result in loss of stored liquids, leakage of hazardous materials, concrete deterioration, and corrosion of reinforcing bars causing serviceability failures. Concrete liquid retaining tanks have a stringent serviceability requirement in terms of limiting crack widths. It is important to note that such cracks are seldom indicative of structural failure and for the purpose of this article we will be limiting the discussion to non-structural and non-corrosion cracks

Shrinkage and differential thermal expansion and contraction due to temperature and other environmental gradients in the exposed surface usually result in restrained movement of the RCC and tends to cause vertical and diagonal cracks in liquid containment structures. It is important to appreciate that not all cracks require repair and reader may refer to ACI 224R, Table 4.1, for crack widths that require repair or remediation.

Liquid containment structures, such as large rectangular tanks, often exhibit vertical and diagonal cracks that are usually the result of restrained concrete shrinkage and thermal contraction, typically spaced 1.2 to 3 m apart. Additionally, such structures may have concrete roof slabs that keep the structure liquid-tight to prevent contamination of the contents by exterior exposure. In these cases, differential shrinkage and thermal deformation of the concrete could result in significant wall and roof cracking if the appropriate expansion joints are not provided. 

Structures with movement joints in the walls and without matching joints in the base slab are prone to crack development not only in the walls adjacent to the joint, but also in the base slab below the joint. Due to the restraint of the base slab, the cracks typically extend diagonally, vertically, or both, and occur on both sides of the movement joints. The width and spacing of cracks depends on concrete shrinkage and creep, the size and spacing of horizontal reinforcement, wall thickness, height and length of each placement (distance between vertical construction joints), and length between movement joints, member restraints, and the concrete mixture. Crack widths can be controlled with appropriate reinforcement and detailing that result in tight cracks that do not leak.

Fig. 1: Typical Cracking in Liquid Retaining Tank

Recommended Best Practices For Repair Of Vertical And Diagonal Cracks In Liquid Containment Structures

Prior to selecting a repair methodology, the cause of the cracks is required to be analysed. It is important to classify cracks as active or dormant and determine if corrosion is active in cracked areas. Shrinkage of concrete continues over an extended period of time and the resulting shrinkage cracks should be considered active, especially if the structure is subjected to cycles of wet and dry periods. Dormant cracks usually result from an event of limited duration, such as temporary overload conditions during construction. It is important to verify that the cracks are non-structural and unrelated to corrosion of steel.

A. Waterproofing And Repair Treatment To Dormant Cracks

A dormant crack is one whose width does not change with time. In the absence of corrosion, dormant but leaking cracks can be repaired by pressure injection of SUNEPOXY 368TM low viscosity epoxy grout or POLYALK 2M1PTM ultra low viscosity polymeric chemical grout by vacuum injection, or routing and sealing on the interior or exterior wall surfaces, or both.

B. Waterproofing And Repair Treatment To Active Cracks

Active cracks are repaired by pressure injection with chemical grouts or by routing and sealing with a flexible sealant on the interior or exterior wall surfaces, or both. Further it is most important to apply a joint free, liquid applied flexible barrier membrane on the liquid retention side of the wall (positive side) like POLYALK WPTM. Active cracks can be repaired by: 1) pressure injecting of chemical grouts; 2) routing and sealing of cracks; and 3) installing a flexible waterproofing and barrier system. These methods are considered serviceability repairs and not structural repairs.

Active cracks are repaired by pressure injection with chemical grouts or by routing and sealing with a flexible sealant on the interior or exterior wall surfaces, or both. Further it is most important to apply a joint free, liquid applied flexible barrier membrane on the liquid retention side of the wall (positive side) like POLYALK WPTM. Active cracks can be repaired by: 1) pressure injecting of chemical grouts; 2) routing and sealing of cracks; and 3) installing a flexible waterproofing and barrier system. These methods are considered serviceability repairs and not structural repairs.

i) Chemical Grout Injection — Injection of flexible hydrophobic polyurethane foam grout material SUNAQUASEALTM is often used for the crack repair in containment structures. SUNAQUASEALTM retains most of its volume after curing, even if the surrounding concrete should become dry, which is advantageous for repairing active cracks. Typical hydrophilic grouts tend to shrink when allowed to dry out and lose volume, resulting in active leaking when the liquid is reintroduced at a later time.

Fig. 2: Grouting Cracks with SUNAQUASEALTM

SUNAQUASEALTM can be used to mitigate leaking cracks with injection performed from the exterior side of a liquid containment structure so the tanks need not be emptied. Interior injection can also be accomplished without draining the tank by experienced divers performing the work underwater. Some excavation may be required to access cracks below grade. When leakage is present, injection using a water-activated resin like SUNAQUASEALTM is recommended. The leakage of water will be slowed down, and possibly stopped, during the injection process.

For tanks containing potable water, chemical grouts and other repair products directly exposed to the water must comply with CFTRI requirements for use in potable water.

For extensive cracking below grade, the application of a waterproofing system might be necessary. There are conditions, however, where injection from the inside wall face is especially recommended to prevent liquid exfiltration, which could require the tank be emptied. Injection from the inside, also provides access for crack repair below grade for buried or partially buried structures without excavation.

The proper climatic condition is crucial for successful crack injection, especially if SUNAQUASEALTM polyurethane chemical grout is used. In cold climates, it is best to complete work at moderate temperatures. Additionally injection in the summer when cracks are the narrowest should be avoided. Repairing cracks in the winter, when they are the most open, is beneficial but costly in case of freezing temperatures. Special heated enclosures could be required to facilitate proper injection and setting of the injection material in freezing conditions.

Crack injection should not be used to repair cracks caused by corrosion of steel reinforcement unless supplemental means are used to mitigate the cause of the cracks and corrosion. If corrosion is present, it should be evaluated before making repairs. This article does not cover repair of cracks resulting from steel corrosion. There are various methods to mitigate, prevent, and control corrosion of reinforcing steel in concrete (ACI 222R) which may be referred to as required.

Injection penetration can be assessed by extracting core samples that intercept the repaired cracks. Usually, one or two cores taken at random locations for every 30 m of injection is adequate as per ICRI guidelines. Typically, penetration is considered adequate if 90 percent of the crack is filled with injection grout. Although, some non-destructive acoustic test methods may be used in some circumstances for testing epoxy adhesive injection repairs, it is not recommended to use these methods for flexible injection materials because the presence of low-modulus materials in cracks and voids do not significantly change the acoustic response from the structure.

ii) Routing And Sealing — with a flexible sealant, incorporating details that permit some movement. Because routing and sealing are performed on the liquid side of the containment structure for tank leakage, the structure should be emptied. In some cases, routing and sealing cracks on the exterior side can be used to reduce the potential for contaminants penetrating the containment structure.

C. Waterproofing Of Liquid Retaining Tank By Installation Of A Liquid- Applied Joint Free Flexible Membrane (Barrier) System

ELASTOROOF PUTM is the most effective and durable treatment to repair and prevent containment structures from leaking. This method is preferred for large tanks which need a long term and durable solution. The tank should be completely empty, and allowed to dry (surface moisture < 4%) before application of the barrier liquid membrane system. ELASTOROOF PUTM is applied in two coats over a suitable primer, and allowed to cure for 48 hours. The resultant barrier membrane is strong, joint free, highly flexible and elastic and extremely durable.

ELASTOROOF PUTM manufactured by Sunanda Global is a single component, high build, liquid applied polyurethane chemistry was adopted as the technology of choice for the waterproofing coating system. This material chemistry offers significant benefits and is able to waterproof 100% in the most trying conditions.

Due to their high mechanical properties, elongation and flexibility, particularly at lower temperatures, as well their capability to cure under a wide range of conditions, ELASTOROOF PUTM polyurethane based liquid applied membranes can also be used in a diverse range of climatically challenging environments. Unlike other waterproofing systems like sheet membranes and acrylic/cementitious liquid applied membranes, this ELASTOROOF PUTM polyurethane application requires comparatively less skill and supervision. As being a liquid applied membranes, ELASTOROOF PUTM cures to a joint free barrier membrane which is especially important in case of large spans/slabs/areas and pre-cast construction projects. Application is fast and curing of the ELASTOROOF PUTM membrane is also quite rapid making the system rain resistant almost immediately after application. Further, the rapidity of the curing reaction enables for speedy over coating and further laying of the protective course. Single component chemistry saves time and eliminates the risk of mixing errors and make the product easy to use.

Considerations For Tanks Containing Aggressive Materials

When chemicals such as acids, alkalis, or process contaminants are present in the liquid contained by the structure, the materials used to inject the cracks should be carefully selected for compatibility and chemical resistance. The sensitivity of materials to acid and alkali-driven chemical attack depends on their composition, the containment chemistry, and the severity of exposure conditions, such as concentration and temperature.

Repair materials are prone to deterioration by permeation if solvents in the tank are close to the solubility of the repair material. The lower the molecular weight of the solvent, the more rapidly it diffuses into the repair material. Crack repair material should be resistant to chemical attacks and other detrimental effects to avoid corrosion. Testing, consultation with the material supplier, or both, is recommended to address chemical compatibility and chemical resistance.

When liquids being contained are corrosive and chemical deterioration of the crack repair materials is expected, additional barrier linings may be required to assure long-term performance of the repair.

References:

1. ACI PRC 364.12T-15: Repair of Leaking Cracks in the Walls of Liquid Containment Structures
2. ACI 224.1R-07 – Causes, Evaluation and Repair of Cracks in Concrete Structures
3. ACI 222 R – Guide to Protection of Reinforcing Steel in Concrete against Corrosion
4. ACI 515.2R – Guide to Selecting Protective Treatments for Concrete