Study On Preparation Of Aerated Concrete With Alkali-activated Phosphorus Slag

Phosphorous slag is a by-product from the production of yellow phosphorous. It was reported that at least more than 5,000,000~6,000,000 ton phosphorous slag was discharged annually in China. Large amount of phosphorous slag was exposed to atmosphere, which not only occupied land and caused pollution in environment due to P and F elements in phosphorous slag, but also wasted some resources. Phosphorous slag contained silicon oxide and calcium oxide has potential activity, so it is significant to make the best use of phosphorous slag. Aerated concrete was made by phosphorous slag with alkali-activator in this research, which was a kind of wall material with the unique properties of lightweight, heat preservation and insulation, sound insulation, fireproofing and easy to process.The influence of powder composition to slurry pouring and some factors that influenced the bulk density of phosphorus slag aerated concrete were studied in this paper, as well as the influence of curing age to compressive strength. The results showed that when powder has 5%~8% of cement and 15%~20% of fly ash, the slurry of aerated concrete is propitious to pouring and molding. The bulk density can be controlled in 500~800kg/m3 when the foaming agent is 0.01%~0.40%, the modulus of sodium silicate is 1.2~1.4, alkali content is 6.0% and the ration of water to the power of solid is 0.29~0.33. The compressive strength of aerated concrete in bulk density of 525~769kg/m3 in standard curing reaches 3.3~7.6MPa, conformed to the standard of autoclaved aerated aoncrete blocks.According to the testing methods of properties about autoclaved aerated concrete, some properties of phosphorus slag aerated concrete such as physical property, recycle freeze-thaw, drying shrinkage and heat preservation property etc were studied in the paper. The results show that as common aerated concrete, hole diameter of phosphorus slag aerated concrete is 1~2mm, porosity is 70%~80%, water-containing is 22.7%~32.3% and water-absorption is 37.0%~51.5%. Shrinkage of phosphorus slag aerated concrete after saturation is above 2.0mm/m, but it is not dangerous in real use because most partly of shrinkage is occurred in the area of water-containing below 5%, and the equilibrium moisture content of aerated concrete material in south is above 5%. Compared to common wall material, it is superior in heat-insulation and heat-insulated. Results of XRD, TG-DSC and SEM showed that main hydration products of the phosphorous slag aerated concrete are C-S-H. Mechanism of alkali-activated phosphorous slag material is also discussed in this paper. Results of IR indicate that the process of hydration of alkali–activated phosphorous slag material is dissolution and polymerization, namely silicon-oxygen bond and aluminum-oxygen bond parted, dissolved and then polymerized.After freeze-thaw cycles and wet-dry cycles, the compressive strength and weight of the blocks reduced obviously, the results showed that the durability of phosphorus slag aerated concrete should be under improved.