Study On The Cementitious Materials With High Porosity And Low Alkalinity

Cement based materials are the largest consumption in exchanging of matters and powers between human beings and nature. Their production, usage, and performance affect the environment of the earth, the resources, the consumption of the powers and the quality of the space. For a long time, people pay much more attention to meeting the special needs, and pay less attention to considering the environment, such as in favor of the environmental protection and the ecological balance while producing and using cement based materials, and mitigate the burden of the environment to the best of their abilities. Few researches have been done from the viewpoint of nature, environment, and the ecological balance. In the 1980's, all of the world concentrates on protecting the environment of the earth, seeking in harmony with nature and tracking the sustainable development. As the most consumption of constructing materials, the future trends of the concrete should not only satisfy the needs of the people but also consider the environment that can alleviate the burden to the earth, save recourses and keep the balance of the ecology. It is the one of the important aspects, which can rebuild the ecological environment such as managing the desert, controlling the water and changing the circumstance of the city by using cement based materials.In order to rebuild the ecological environment using the traditional cementitious materials, low alkaline fly ash porous concrete, no fines concrete and the high porosity no-fines concrete were investigated from the two aspects of forming the high porosity and reducing the alkalinity. The relationships among the composition, microstructure and performance of these cementitious materials with high porosity and low alkalinity were studied. At the same time, the plant growing on these kinds of cementitious materials was also studied. The study shows that:In the system of cement-fly ash-lime-water with aluminum powder which producing gas, the content of lime is the most important factor, because it affects thet/ABSTRACTpH value of the low alkaline fly ash porous concrete. With the adding of the content of lime, the pH value in the pores raises sharply. The content of aluminum powder is the main factor of affecting the porosity, the unit mass and the water absorbability of the low alkaline fly ash porous concrete. With the increasing of the aluminum powder, the porosity of the fly ash concrete increases, the unit mass reduces and the water absorbability enhances. If the compressive strength was neglected, the concrete , which was made by 1.2%o of aluminum powder, 0.60 of water binder ratio, 10% of cement, 15% of lime, 75% of fly ash, meets the request of low alkaline, high porosity. The porosity of the concrete is 27.74%, and the pH value is 8.92.The compressive strength of the low alkaline fly ash porous concrete in 90 days can improve 20%~30% comparing with 28 days, and its pH value can reduce 1.5~2.0 for the reason of carbonation and the secondly pozzolanic reaction, it is demonstrated that the main hydration products is calcium carbonate and calcium hydroxide by the analysis of XRD, SEM, EDXA. The distribution of the pores is uniformity and the size of the pores is identical. The shape of the pores is mainly roundness and the wall of the pores is lubricity. The pores are continuosly and its diameter is about 0.5mm.The porosity of the no-fines porous concrete which was prepared by the continuous aggregates is more than 30% and the 28 days compressive strength is greater than lOMPa. It also satisfies the requirement of high porosity. When the cement to aggregate ratio and the ratio of water to cement are fixed, with the particle size reducing, the compressive strength improved and the porosity decreased.The compressive strength of the no-fines porous concrete, which was prepared by the continuous aggregates and single aggregates, increased and the porosity receded with the ratio of water to cement increased from 0.26 to 0.35. When the water to cement ratio is fixed, with the cement to...