Study On Alkali Activated Phosphorous Slag-Flyash Cementitious Material

The utilization of alkali activated phosphorous slag cement and fly ash in concrete industries has a promising prospect because of its environment-friendly origins and ability to enhance cement's properties. A new alkali-activated phosphorous slag-fly ash cement material (APFA) has been developed as the initial result of a profuse experiment, which is comparable with the 42.5 ordinary Portland cement (OPC) in general physical properties, and behaves more excellently than 42.5 OPC in some special aspects, such as resistance to various chemical attacks, freezing and thaw deterioration. A detailed examination and analysis on the physicochemical feature of the phosphorous and fly ash as raw materials for the APFA cement material and on the microstructure of the hardened APFA cement material paste have been carried out by means of XRD, IR, TG-DTA, BET, SEM and Mercury Intrusion Porosimetry (MIP) measurement as well as chemical analysis.Various factors were studied which will affect the amount of water, the time of concreting and the strength of the cement of alkali-activated fly ash/slag. The experiment design involved: the amount of the water glass ( assayed with the Na₂O:4%,5%,6%);the modulus of water glass (1.2,1.4and 1.6);the amount of fly-ash mixed into the material (0%> 5%, 10%, 15 % , 20%). The product with optimum proportion of phosphorous slag to fly ash ratio 85:15 and addition of composite activator mode 5%⁶% showed high early strength development and high ultimate strength and an appropriate setting behavior, i.e. the initial and final setting time being about 117min and 151min respectively, the 28d mortar flexural and compressive strength being 9.8MPa, 78.1MPa respectively. In addition, there is no any indication referred to the strength decrease during the curing to be found. Moreover, APFA cement represent a better volume stabilization, a better resistance against chemical attack and freezing and thaw deterioration than OPC, which implies that it is possible for APFA cement to be used in some severely aggressive environment where OPC does not suffice, e.g. harbors, piers, chemical plants, etc.Moreover, the microstructure of the cement of alkali-activated fly ash/slag isanalyzed by means of BET, TG, SEM, the mechanism of activation of slag and fly-ash is also studied. Meanwhile, the hydration process of slag and fly-ash mixed with activator is explored in theories on the basis of the analysis about the morphology and chemical composition of the hydration products and the microstructure of the hardened cement paste. The characteristic of the C-S-H with low Ca/Si and the absence of the crystallized Ca(0H)2 therefore become its chemical origin while the low porosity and the good pore size distribution feature become its physical origin for its good physical properties and good resistance to chemical attack.