COMPOSITE POLYMERICADDITIVESDESIGNATED FORCONCRETEMIXES BASED ONPOLYACRYLATES, PRODUCTS OF THERMAL DECOMPOSITION OF POLYAMIDE-6 AND LOW-MOLECULAR POLYETHYLENE

The goal of the present research is to develop polymeric additives based on aqueous dispersions of (meth)acrylic polymers, including polymethacrylates, polyacrylates, products of thermal decomposition of polyamide-6 in the vegetable oil media, and low-molecular polyethylene. Decomposition of polyamide-6 took 8…10 hours at the temperature of 245…275 °С. The mixture of low-molecular polyamides, the average molecular weight of which reached 3400…8600, was used both independently and as a constituent of a composite additive designated for Concrete Mix В 22,5 (М300). The choice of polymers is based on their availability, as they are produced by local manufacturers of chemicals. For example, low-molecular polyethylene is the by-product of high-capacity synthesis of high-pressure polyethylene. Besides low-molecular polyamides, additives may represent concentrated oligomers of ε-caprolactam generated in the course of synthesis of polyamide-6. Therefore, the problem of disposal of by-products generated by major producers of chemicals is resolved to some extent, while the cost of the feed stock required for the manufacturing of effective additives designated for concretes goes down. The above substances are non-toxic, they do not emit any hazardous fumes in the course of the concrete mixture preparation, further evaporation and dehydration of molded concrete and reinforced concrete products. Therefore, the following conclusions can be made on the basis of the research of the influence of polymeric additives onto the properties of Concrete В 22,5: 1) polymeric additives 1, 2, 3, 4, 5 represent plasticizing additives that decelerate the hardening of concrete mixtures and reduce the water-cement ratio by 6.5 % (Additive 1) - 19.4 % (Additive 5); 2) Additives 1, 2, 3, 4, 5 added into the mixture in the amount of 0.5…0.7 % (weight share) improve the strength of Concrete В 22,5 samples, if tested on the 28 day of hardening (see Table 1) in the dry-hardening mode, if compared to the benchmark sample, by 0.6% (Additive 1),by 9.1% (Additive 2), by 22.4% (Additive 3), by 24.8% (Additive 4), and by28.2% (Additive 5); 3) polymeric additives improve the water resistance of Concrete В 22,5 by 2.56 times (Additive 1), by 7.5 times (Additive 2),by 26,2 times (Additive 4), by 191…195 times (Additive 5), if compared to the benchmark sample; 4) the optimal composite additive that increases the time period of stiffening of the cement grout , improves the water resistance and the compressive strength of concrete, represents the composition of polyacrylates and polymethacrylates, products of thermal decomposition of polyamide-6 and low-molecular polyethylene in the weight ratio of 1:1:0.5