Features of using cement suspension in concrete mixture recycling technology

Introduction. Recycling technologies may solve the problem of landfill waste. The problem of hydraulic active cement waste using not fully resolved in concrete mixtures recycling technologies. Using hydraulic active cement waste as an addition directly influences the technological and mechanical characteristics of new concrete mixtures. That requires additional research. Materials and methods. The cement waste obtained after recycling was simulated by pre-hydrated cement suspension produce at V/C equal to 0.7 for 6 hours of hydration. Different compositions of cement mixtures were investigated. The difference of which was amount of introduced pre-hydrated cement additive, both in the presence and without plasticizer. Technological properties, namely the normal consistency and setting time of cement compositions were investigated by standard methods of GOST 30744-2001. Mechanical properties, namely the compressive strength at the age of 28 days, were determined by destructive method on a hydraulic press PSU-10. Results. The introduction of a pre-hydrated suspension causes an increase in normal consistency, a reduction in the setting time and a decrease in strength with an increase in its quantity. The use of such a suspension in conjunction with a superplasticizer can level out the increase in normal density, as well as increase the strength of the samples. Timing of setting remained similar to the results of the test without the plasticizer. Conclusions. The results of the study show influences of cement waste obtained after recycling on the technological and mechanical characteristics of new mixtures. These influences are important and must be taken into account in the design of new concretes and mortars.