The influence of the water-cement ratio and polymer latex on the mobility of the self-compacting mixture and on the strength characteristics of concrete
Reinforced concrete hydraulic structures of water management and ameliorative complex in the course of operation are exposed to various aggressive factors, are destroyed and require repair and restoration work using the technology of monolithic concreting. One of the most promising materials that can be used in the repair and reconstruction of hydraulic structures is self-compacting concrete - concrete based on concrete mixtures of high mobility, capable of being compacted by its own weight without the use of vibration energy. Such mixtures are obtained by modifying traditional concrete mixtures with organo-mineral additives based on polycarboxylate superplasticizers and active mineral additives (silica fume, metakaolin). The use of self-compacting concrete mixtures allows to conduct concreting in hard-to-reach places, in conditions of high saturation of structures with reinforcement and to obtain concrete with high strength.
Analyzing the results of known studies, we can conclude about the positive effect of the complex modifier "superplasticizer - active mineral additive" on the properties of concrete. At the same time, self-compacting concrete based on known formulations has drawbacks: insufficiently high rates of crack resistance, adhesive strength and impact strength. To eliminate the noted deficiencies, we proposed further modification of self-compacting concrete with polymer latex. Its role in the formation of the structure and properties of concrete at various values of the water-cement ratio has not been studied enough.
The aim of the work is to study the effect of the water-cement ratio and additives of polymer latex on the mobility of self-compacting concrete mixtures and on the physico-mechanical properties of concrete based on them.
The studies used: Portland cement brand 500, crushed granite fraction 5-10 mm, river sand with a modulus of 1,86, polycarboxylate superplasticizer Adium 150, silica fume “Elkem Microsilica”, polymer latex Adiplast. Concrete mixes were prepared using a hand-held electric mixer in three stages: first, dry components were mixed for 5 minutes. Then prepared the liquid phase by mixing water, superplasticizer and polymer latex for 5 minutes. At the end, the mixture of dry ingredients was mixed with the liquid phase for 5 minutes.
The consumption of the components of the control composition of concrete was (kg per 1 m3): Portland cement - 450; sand - 940; crushed stone - 940; silica fume - 45; superplasticizer - 7.2; water - 135.
Concrete samples were formed by pouring mixtures into the appropriate forms and kept in normally-wet conditions for 28 days.
Testing of concrete mixes and concretes was carried out according to methods known in concrete science. The compressive strength of concrete was determined on samples-cubes of 7,07×7,07×7,07 cm, flexural tensile strength on samples-beams of 4×4×16 cm, axial tensile strength on samples of eight with a cross-section of the middle part - 2, 25x2,25 cm, with a total sample length of 7,8 cm, impact strength on sample cylinders 5 cm high and 2,5 cm in diameter.
Analysis of the research results shows that the water-cement ratio and the content of polymer latex in the concrete mix is an important factor in the formation of the structure and properties of self-compacting concrete. By reducing the water-cement ratio from 0,4 to 0,3, the spreading of the cone of concrete mixes decreases from 790 to 540 mm, the compressive strength of concrete increases from 64,6 to 74,3 MPa, the bending strength - from 8,8 to 10, 9 MPa, tensile strength - from 3,52 to 3,94 MPa. Polymer latex has a positive effect on bending strength, tensile strength, impact strength and crack resistance of concrete. With the introduction of polymer latex in the concrete mixture in an amount of from 3 to 9% by weight of cement (dry residue), the bending strength of concrete increases by 4 ... 15%, tensile strength - by 12 ... 18%, impact strength – 2,2...2,75 times, the coefficient of crack resistance – 1,3...1,8 times. The introduction of latex into the concrete mix in the amount of 3% leads to a decrease in the compressive strength of concrete by 15 ... 20%, 6% - by 21 ... 30%, 9% - by 39...42%.
When the content of polymer latex in concrete mix is 3 ... 6% by weight of cement, water-cement ratio from 0,35 to 0,38 and cement consumption is 450 kg/m3, self-compacting polymer cement concrete is characterized by the following technological and physico-mechanical properties: spread of a cone - 550...800 mm, compressive strength - 45 ... 55 MРa, bending strength – 9,3...10.8 MРa, tensile strength – 4,3...5,4 MРa, impact strength – 0,39...0,43 MРa, coefficient of crack resistance – 0,1...0,2.
These characteristics indicate that self-compacting polymer cement concrete is a promising material for structural repair of concrete and reinforced concrete hydraulic structures.
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