Preparation And Performance Study Of Pervious Alkali Activated Slag Concrete

Pervious concrete(PC)is composed of cementitious material,coarse aggregate,water and admixture.It has a lot of connected pores,so it is breathable,permeable and aquiferous.It can alleviate the urban-heat-island effect,localized flash flooding and recover rainwater to replenish groundwater,improve the traffic environment,very economical and environmentally friendly,has obtained a lot of research and the application.However,it still has many problems,including low strength,poor durability,easy clogging,easy cracking,etc.These problems restrict the further application of PC.Alkali activated slag has the characteristics of high strength,fast hardness and good durability,it will improve the interface bond strength between the aggregate and the slurry,so as to effectively avoid the dispersion of the aggregate and improve the strength and durability of pervious concrete.In this paper,the volumetric design method was used for pervious alkali activated slag concrete mix design.The samples were cast in two layers,15 blows per layer ramming from the edge to the center and flattened with the surface vibrator,scraper.The basalt gravel with good quality was selected for the aggregate.The influence of designed porosity,slurry composition and aggregate performance on the strength,pore content,and water permeability of pervious alkali slag concrete was experimentally studied.The main conclusions of the research are as follows:(1)The strength of alkali activated slag develops rapidly,and promote the strength development of PC.Tests have shown that the 7d compressive strength of pervious alkali activated slag concrete can reach 69% to 88% of 28 d,and increases continually from 28 d to 60 d.(2)The strength of pervious alkali activated slag concrete increases with the increase of the of alkali slag strength and paste film forming thickness.When the designed porosity is too large or too small,the impact of the difference in slurry strength on the strength of concrete will be reduced.(3)The rheological parameters of the slurry,including the viscosity coefficient and the yield stress,have an effect on the workability of the PC mixture and PC strength and permeability after hardening.The increase in yield strength resulted in paste film forming thickness increase;the decrease of AAS paste viscosity coefficient can modify workability of mixture,improve PC density and enhance PC strength.The proper incorporation of silica fume can not only improve paste yield stress,but also dense the bond between the slurry and the aggregate.Incorporate 10% silica fume,the fluidity of the slurry was reduced to 120 mm,but the compressive strength of PC was increased from 26 MPa to 41.9 MPa,and the splitting tensile strength was raised from 2.55 MPa to 3.71 MPa,and the water permeability was 10.4 mm/s.(4)When the designed porosity is 21%,the compressive strength of PC prepared from different sizes basalt gravel is: 5 ~ 10 mm >10 ~ 16 mm >2.5 ~ 5 mm.When the 5 ~ 10 mm and the 2.5 ~ 5 mm grain size aggregate are mixed in different ratios,the compressive strength decreases to varying degrees,even lower than that of the two single grades.(5)Mixing 30% of irregular aggregates into aggregates of the same size will improve the compressive strength,splitting tensile strength and slightly decrease permeability of 5 ~ 10 mm and 10 ~ 16 mm sizes,but it has no obvious effect on the 2.5 ~ 5 mm size aggregate.After the basalt crushed stone is shaped by ball mill,the irregular edges and corners are removed to different extents,and the accumulation of aggregates is more compact,and can produce higher strength pervious concrete..With the increase of aggregate shaping time,the compressive strength and splitting tensile strength increased significantly.However,due to the increased packing density,the pore content and water permeability decreased.When shaped for a long time the surface of the aggregate is too smooth,and new cracks and defects may occur,which are not conducive to the adhesion of the slurry and the aggregate.Therefore,the shaping time should be controlled within 35 minutes.