Hybrid Superplasticizer for High Performance Concrete
Mayank Rawal
Managing Director
Asian Laboratories
In recent years, there has been increasing interest in durability. In particular, reduction in shrinkage cracking of reinforced concrete to increase life-span extension of reinforced concrete structures.
The shrinkage of concrete can adversely affect not only its fitness for use but also the durability of concrete structure elements. It is suggested that materials such as Lime Stone aggregate expensive additives & shrinkage – reducing admixture be used effectively as a measure to reduce drying shrinkage which is one of the major issue of cracking in normal strength concrete.
On the other hand, high strength concrete has been used for high-rise reinforced concrete in housing and urban areas. Higher strength generally requires higher binder content which leads to autogenous shrinkage, for this reason, measures to reduce autogenous shrinkage of high- strength concrete have been required in order to prevent early age cracking caused by autogenous shrinkage.
Therefore, in order reduce shrinkage cracking of concrete; we at Asian Laboratories have developed Hybrid Admixture: CEMWET SP-3000 PCE-SR Superplasticizer with shrinkage reducing properties. The results of concrete testing in the lab reflect reduced drying & autogenous shrinkage in concrete.
Material
The materials used in experiments are summarized in Table 1. Ordinary Portland Cement as per IS 269:2015 was used for the tests. The cement has a Blaine fineness of 368m2 /Kg. Polycarboxylic Ether based commercial Superplasticizer was used for this test.
CEMWET SP-3000 PCE-SR which been developed by our research group is a Hybrid Superplasticizer with high water reduction performance and a good shrinkage reducing effect which was also used for the tests. The molecule structure is shown in Fig. 1.
Table 2 describes the mix proportion for measuring shrinking of concrete. In the design of concrete mix sand of ZONE-2 having fineness modulus of 2.6 and gravel of maximum size of 20 mm were used with approx. 40% of sand and 60% Gravels by mass respectively.
Test of Fresh and Hardened Concrete
The concrete specimens were prepared and stored according to IS:9103-2000. Concrete setting time, water reduction and compressive strength were tested at 3 Days, 7 Days & 60 Days. The details of mixed designs are given in Table 4 as under.
Shrinkage Measurement
Measurement of the early age (before 1 Day) shrinkage of concrete under sealed conditions. Early age testing began approximately 30 min. after water addition to the concrete mixing process. The fresh concrete was placed in the 100 x 100 x 515 mm steel mold and consolidated with external vibrating table. This beam is tested for the settlement shrinkage of concrete at the age of initial 24 hours.
1. Non-Contact Sensors
2. P-P Inner Line
3. M-S Pipe
4. Temp. Sensor
5. Plate Form Slab
6. Recorder
Measurement of the Long-Term Shrinkage of Hardened Concrete
One batch of concrete specimens for measuring long term shrinkage of concrete was casted in the 100 x 100 x 515 mm prismatic steel molds. After demolding, specimens were cured in a room at constant temperature (25 ± 2o C) and a constant relative humidity level (>90%) for 2 days. Then after initial reading the specimens were exposed in a controlled room temperature of 25 ± 2o C with a constant relative humidity level of 60 ± 5 %. The length changes were monitored by micrometer at different time intervals up to 60 days.
Another batch of concrete specimens for measuring long term autogenous shrinkage of concrete was casted in the 100 x 100 x 515 mm prismatic steel molds with double inner polypropylene film. Immediately after casting, a layer of soft impermeable polypropylene film was covered on the surface of specimen. Just after demolding at the age of 1 day the samples were first placed in the 110 x 110 x 550 mm cuboids iron barrel, further the empty surface space is filled with the liquid paraffin in order to avoid moisture loss with the surroundings. After the initial length measurement, specimens were exposed in the curing room maintained at 25 ± 2o C & relative humidity 60 ± 5%.
The length change was monitored by micrometer (Fig. 3) at different time interval up to 60 days.
Results
Concrete test results are shown in Table 4. The results shows that the hybrid PCE with shrinkage reducing properties is able to perform better in water reduction and shrinkage reduction compared to the normal commercial PCE. When 0.2% of CEMWET SP-3000 PCE- SR was added, the water reduction was up to 25% as compared to the reference mix while the water reduction at the dose of 0.3% was approximately 30.1%. Commercial PCE dosages are required to be higher for equal water reduction. The setting time of concrete is retarded with commercial PCE. However, the CEMWET PCE SR containing shrinkage reducing functional group shows little retarding compared to the control concrete. Fig. 4 shows the effect of admixture type on settlement shrinkage. The data shows that CEMWET-PCE SR decreases the settlement shrinkage effectively.
Figs. 5, 6 & Table 5 shows the effect of admixture on long-term drying shrinkage compared with normal PCE at a dosage of 0.3%, CEMWET SP-3000 (SR) at a dosage of 0.25% decreases the drying shrinkage by 41.4% at 28 days and 41.9% at 60 days.
Similarly, long term autogenous shrinkage is reduced by 52% at 28 days and 51% at 60 days compared with normal PCE at a dosage of 0.3%.
Fig. 4: Settlement of Shrinkage of Concrete
Fig. 5: Long Term Drying Shrinkage of Concrete
Fig. 6: Long Term Autogenous Shrinkage
Conclusion
The performance of Hybrid CEMWET PCE SP-3000 (SR) is better in water reduction & shrinkage reducing effect.
The product can reduce water up to 30% at a dose of 0.25% by weight of cement. However, the setting time and strength are quite remarkable.
The early age shrinkage at 1 day is reduced by 43% compared with normal PCE Superplasticizer. The autogenous shrinkage of concrete is reduced by 52% at 28 days and 51% at 60 days respectively.
The drying shrinkage reduces by 41% at 28 days and 42% at 60 days respectively. Newly developed shrinkage reducing superplasticizer can be used where cracking needs to be minimized.
References
C. K. Nmai, R . Romita , F. Hondo and J. Buffenbarger: Concrete Int. 4 (1998)
S. Nagataki and H. Gomi: Cement and Concrete Composites. 20 (1998)
J. Engstrand: Con. Chem. J. 4 (1997) 149-151 3. Rawal, MK: “Role of Superplasticizer in Concrete” National Seminar on Performance Enhancement of Cement and Concrete by use of Fly Ash, Slag, Silica fume & Chemicals – (1998)
Rawal Mayank: “High Performance Admixture on Superplasticizer for Concrete”. Proceedings of ICFRC. International Conference on Fibre Composites, High Performance Concretes & Smart Materials – (2004)
Rawal Mayank: “Recent Development in Admixture for the Underground Construction”. Superplasticizers & Other chemical Admixtures in Concrete- 12th International Conference, Beijing – (2018)
