Preparation Of Fly Ash-based Lightweight Wall Materials: An Experimental Study

Wall materials are 70% of the building materials in China, and the red bricks are the main wall materials. Production of red bricks will destroy the plantation, consume too much energy and pollute the environment. So, we must empolder various kinds of new wall materials, and they should saving the plantation, consume little energy, using the waste, and be propitious to our environment.Geopolymer (or mineral polymer), a new category of inorganic nonmetal materials developed in recent years, which is manufactured mainly from various aluminosilicate minerals or industrial solid wastes by former researchers, has such advantages as fast hardening, high intensity etc.In this experiment, the fly ash, with lime, sodium silicate, NaOH and CaSO4 as assistants, were used to prepare a new kind of geopolymer, i.e. lightweight loadbearing wall materials. The materials was manufactured by wet-grinding, molding and then curing at 192℃, 1.3MPa for 10 hours in autoclave.The current experimental results show that the optimal raw materials proportions are: lime 12%, sodium silicate 10%, NaOH 2%, CaSO4 3%, the mass ratio of the solid to liquid is 2.0. The compressive strength of the representative products reach up to 14.68±1.66MPa, and the volume density was 1.11±0.03g/cm~3, the thermal conductivity coefficient is 0.12W/(m·℃). The water content and water absorbability of the representative products were 19.84±0.06% and 44.42±0.23% respectively. The compressive strength of the products are higher than the MU10 standard requirements of the red bricks, the volume density are only 2/3 of the red bricks, the adiabatic capability were improved and therefore, could be used as lightweight wall materials, instead of the red bricks.The XRD analysis and the microstructure characteristic of products show that the matrix of mineral polymer products is amorphous phase, the crystal phases of the materials are mullite, tobermorite and plazolite.During the solidification of the mineral polymer products, both of silicate and aluminate oligomers formed by Si-Al materials in the alkaline solution and the force of grinding produced aluminosilicate gel by dehydroxy polymerization, then transformed into a three-dimension network structure matrix with Si-O-Al-O bonds, leading to excellent mechanical properties for the mineral polymer products. The silicate and aluminate oligomers are also reacted with CaO and formed calcium silicate hydrate and calcium aluminate hydrate which transformed into tobermorite and plazolite in the age of curing in autoclave. These tobermorite and plazolite formed lots of pores in the materials, leading to well adiabatic capability for the products.