Study On The Influence Of Tuff Power Admixture On The Performance Of Hydraulic Concrete

The high quality admixture is widely used in the hydraulic concrete to reduce the dosage of cement and improve the concrete performance, and it is the indispensable component of hydraulic concrete. With development of water conservancy construction in the southwest China, as a result of the limitation of local economic development level and traffic facilities, raw material supply shortage become an important problem occurred in construction engineering where traditional mineral admixture fly ash and slag are scarce. Seeking for natural pozzolanic admixture near the engineering area to replace or partially replace fly ash is an important means to alleviate this problem, which not only ensured the construction to be conducted smoothly, but also can effectively reduce the construction cost. Based on this major fact, systematic experimental studies were carried out about tuff powder concrete admixture, which is a natural pozzolanic material in the middle of yarlung zangbo River in Tibet.Both the macro and micro analysis method were used in this study. The tuff rock mineral identification was carried out firstly. The tuff rock was grinded fine up to severl levels of specific surface area, and tests their physical and chemical indexes and particle microstructure, such as chemical composition, volcanic activity, particle size, water requirement ratio. Then studied the effect of tuff powder on the workability and strength of cement mortar and analysesed its hydration effect. Tested and analysised the effect of tuff powder on properties of concrete. At last, analysised the hydration characteristic of cement paste with tuff powder through means such as XRD, SEM, DSC and TGA. Research results show that:(1) The potential active ingredient content of the tuff powder is high, Si02 and A1203 accounting for about 80%, without harmful substances. But the XRD analysis shows that there are many low temperature quartz and feldspar which don’t participate in the hydration reaction.(2) Tuff powder fineness has little influence on the water requirement ratio and mortar liquidity but has a greater effect on strength. The finer the tuff powder, the higher the strength of mortar specimens.(3) Tuff particles fill effect makes slurry microstructure better in the early age and structure tightly bounded in the long-term. The mixed tuff powder has little effect on microtek phase type of hydration products in hardened cement paste. Only the diffraction peak intensity as well as the main hydration products of Ca(OH) 2 total are different.(4) Tuff powder is a new type of mineral admixture, and either single doped or mixed with fly ash, concrete mixed with tuff powder could be configured through the optimization of aw material and mixing ratio to meet performance requirements.