Study Of Alkali-actived Phosphorous Slag Cement

It is believed that alkaline-activated cementing materials deserves more attentions due to their distinct characteristics including no need for high-temperature firing ,wide availability of raw materials (industrial solid wastes), good cementing performance, no pollution, etc. Alkali-activated phosphorous slag cement is a new type of cement which is made of phosphorous slag that is activated by alkali activator, In this work, the activator is water glass.In the first, based on compressive strength, the influence of the specific surface area of phosphorous slag, modules of water glass and alkali content on the mechanical properties of alkaline activated phosphorous slag cementitious materials was studied, and the experiment were conducted in accordance with GB/T17671-1999. Then, based on the results of the compressive strength, some right mix proportions were choosed to research setting time in accordance with GB/T1346—2001, and the influence of the specific surface area of phosphorous slag, modules of water glass and alkali content on the setting time of alkaline activated phosphorous slag cementitious materials was studied. In the end, the optium mix proportion was obtained. The results show that mechanical properities of alkali-activated phosphorous slag cement are better than ordinary Portland cement, and the highest 28d bending and compressive strength can reach 9.3MPa and 102.5MPa. The setting time of alkali-activated phosphor slag cement is short, but they all adjust to the standards of Portland cement. In all, alkaline activated phosphorous slag cementitious material with normal setting performance and desirable mechanical properities can be prepared by using the water glass with the SiO₂/Na₂O module of 1.4 as the activator, the dosage of the water glass equivalent to Na₂O being 5%(w) of total quantity of phosphorous slag, the specific surface aera of phosphorous slag is 380kg/m² .In comparison with silicate cement, two choosen mix proportions were tested accordance with DL/T5150-2001. The results show that alkaline activated phosphorous slag cementitious materials have high anti-penetrating, high resitance to frost and thaw, and to sulphate attacks, but the dry shrinkage coefficients in the early times is a littlebigger. There are no alkali-aggregate reactions happenned in the text. This is due to the pore porosity of alkaline activated phosphorous slag cementitious, and there are too much gel in harden cement. There exist no hydration products such as Ca(0H)2, ettrigite, highly basic C-S-H which are bad for resistance and often found in Portland cement.The phase composition, microstructure and pore structure of hardened alkali-activated phosphorous slag cement paste coated with compressive strength and durability were analyzed by means of MIP evaluation, thermal analysis, X-ray diffraction analysis, infrared spectrum analysis and scanning electron microscope. The main hydration products of alkali-activated phosphorous slag cementitious material were identified as lowly basic C-S-H, but no Ca(OH)2. These products grow in different ways, fill and block the pores, so that the hardened alkali-activated phosphorous slag cement past is much more compact than that the hardened OPC cement paste, and the mean pore size in the former is also much smaller than that in the late one, so that make the mechanical properities and resitance properties of alkaline activated phosphorous slag cementitious materials are better than Porland cement.