Possibilities of plastic waste application in expanded clay concrete

Abstract

The article analysis the application possibility of plastic waste and their impact on the properties of expanded clay concrete. Two plastic waste are selected from SC “Plasta” (A and B types). A type waste has slimy and dense structure, B is more porous and has rough surface. Whereas the average size of waste is up to 1 cm and the bulk density is similar to that of expanded clay, these waste have replaced a part of expanded clay with the fraction of 4/8 (0%, 5%, 10%, 20%) in expanded clay concrete mixtures. Amounts of cement, fine aggregate (sand), 8/16 fraction expanded clay, water and superplasticizer in expanded clay concrete mixtures are constant. Properties of expanded clay concrete are determined and analysed as follows: density and slump of the mixture, density of the dried expanded clay concrete specimens, capillary rate, water absorption and compressive strength. Additionally, microstructure research is conducted. It is determined that using more waste (20%), by 4% denser and by 50% stronger expanded clay concrete may be obtained compared to the control specimens. To obtain expanded clay concrete with optimal properties, it is suggested to use 5% of A type waste instead of calculated amount of 4/8 fraction expanded clay. Then, the density of expanded clay concrete increases by 5% and it is equal to 1260 kg/m3, and compressive strength is by approximately 70% greater than the one of the control specimens and it is equal to 17 MPa. Moreover, the capillary rate and water absorption decrease. When up to 10% of A type waste are used, mixture slump increases and workability improves, therefore, the obtained specimens are easy to form. Microstructure analysis shows that there is sufficient adhesion between aggregates, waste and cement stone. The microstructure of cement stone under different loadings of waste is different. The densest structure has specimens with 5% of A type waste. The same minerals, i.e. portlandite, ettringite, calcite and calcium hydro silicates are determined in specimens from all batches. After conducting statistical analysis of the obtained compressive strength results, mathematical second degree polynomial dependence is concluded. It allows prediction of expanded clay concrete’s compressive strength depending on the amount of waste. Determination coefficient of the equation is equal to 0.845. It can be seen from the obtained equation that the compressive strength of expanded clay concrete increases under a certain amount of waste and then, it decreases.