Geopolymer concrete made using large-tonnage technogenic waste

Abstract

Introduction. Currently, in all countries, Portland cement is used as a binder in the production of concrete, and its global production accounts for 10 % of the total carbon dioxide emitted into the atmosphere. Therefore, Portland cement can be partially or fully replaced by new cement-free binders, made of large-tonnage technogenic waste with a cementing effect, for example, by finely ground blast furnace slag, fly ash generated by thermal power plants and ash formed during the combustion of rice hulls. Aqueous alkaline solutions (NaOH and Na2SiO3 or KOH and K2SiO3) should be used as activators of setting and hardening of such binders, and calcium sulfate dihydrate can be used to adjust the setting time. Concrete containing new cement-free binders is called geopolymer concrete. Materials and methods. In order to reduce mixing water consumption and maintain the required workability of the fine-grained concrete mixture, a polycarboxylate superplasticizer was introduced into its composition. All raw materials, except for the superplasticizer, were of the Vietnamese origin. The following research methods were used: the composition of the geopolymer concrete mixture was analyzed using the absolute volume method, the workability of the concrete mixture was determined according to ASTM C1611-18 и TCVN 3106:2007, compressive and tensile strength of the concrete, subjected to bending, were tested pursuant to GOST 10180-2012, and the average density of concrete was tested according to GOST 12730.1-78. Results. The co-authors have developed the composition of the geopolymer concrete containing the alkaline cement-free binder. As a result of the heat treatment of the 28-days-old concrete for 6 hours at 100 °C, its compressive strength reaches about 60 MPa; hence, it can be used in the hot and humid climate of Vietnam. Conclusions. This cement-free concrete, in addition to its high strength, has good water resistance and low water absorption. This concrete has economic benefits, and its production will help to protect the environment due to the lower consumption of natural resources and the applicability of large-tonnage technogenic waste.