| Porous concrete (POC) is made of single-sized coarse aggregate,Portland cement,admixtures,chemical admixtures,water etal. It should be properly mixed before cast in mould. Because of its large-pore structure, POC have much ecological and environmental value. It can be widely used in river side,highway side,water purification,pavement,voice absorption,organism adaptable structure, and so on. In the case of be used as greening concrete which placed in river side or highway side, POC'S compressive strength should be higher than 15MPa, at the same time its void content should be at the range of 25% and 30%, generally speaking.Firstly , the mixing and casting technology be researched in this paper. While mixing, coarse aggregate should be wetted at first, then put in Portland cement (include admixtures, if use),water (include chemical admixtures, if use) alternately. Mixing time should be controlled within about 4min; It was assumed satisfactory if: (a) a wet-metallic appearance of the mixture is imparted; (b) no cement paste flow away from the aggregate particles; (c) porous concrete does not crumble or void-free after being handful squeezed and released. At this time, the concrete mixture could be placed, and vibrating time should be controlled within about 20s. optimum flow value of cement paste which made POC could be conveniently placed is at the rang of 190mm and 220mm. if use fly ash,slag fume and fine-sand in paste, its shrinkage would be decreased sharply. Below the adding amount of 15%, fly ash and slag fume will benefit to the increase of POC'S compressive strength, But fine-sand is not. If add fly ash,slag fume,fine-sand into paste at the same time, not only the shrinkage of paste would be decreased, but also the compressive strength of paste would be increased.In this paper, the properties of POC are researched with different mix proportion which use different aggregate-binder ratio(A/B),different water-binder ratio(W/B) and different single-sized coarse aggregates. The result is that coarse aggregate's size,A/B and W/B are the main factors which affect POC'S performances. With the same A/B and W/B, POC'S compressive strength decrease when the size of coarse aggregate increase, while POC'S void content increase in this case. Single-sized coarse aggregates are fitter than continuous-grade coarse aggregates. A/B affect POC'S strength and void content at the same time. When A/B increase, the content of paste in POC decrease, which will cause POC'S compressive strength decrease and void content increase, otherwise the result will be just conversely. W/B is a mainly factor in the process of placing; relate to every kinds of coarse aggregates and A/B, there is a optimum W/B fit for it. as far as greening concrete is concerned, select 10mm----20mm coarse aggregate, A/B vary between 4----6 and W/B range from 0.26 to 0.32 will fit for its performance requirements.In this paper, frost resistance of POC is researched. Adsorbing ordinary Portland cement...
|
PDF Full Text Request