The Chloride Permeability of Persulphated Phosphogypsum-Slag Cement Concrete

The chloride permeability and microstructure of persulphated phosphogypsum-slag cement concrete（PPSCC）, the Portland slag cement concrete（PSCC） and ordinary Portland cement concrete（OPCC） were investigated comparatively. Some test methods were used to evaluate the chloride permeability and explain the relationship between the permeability and microstructure of concrete. The results show that the resistance to chloride penetration in PPSCC is significantly better than that in OPCC, the reasons are as follows： 1） the slag in PPSCC is activated by clinker（alkali activation） and phosphogypsum（sulfate activation）, forming more low Ca/Si C-S-H gel and gel pores below 10 nm than OPCC, improving the resistance to chloride penetration; 2） the hydration products of PPSCC have a much stronger binding capacity for chloride ions; and 3） in the same mix proportion, PPSCC has a better workability without large crystals calcium hydroxide in the hydration products, the interfacial transition zone（ITZ） is smoother and denser, which can cut off the communicating pores between the pastes and aggregates.

The Accelerated Test of Chloride Permeability of Concrete

The availability of accelerated chloride permeability test and the effect of w/c ratio, incorporation of silica fume, maximum aggregate size and aggregate type on the chloride permeability were studied. The mathematic analysis certifies that there is a linear relationship between accelerated test and natural diffusion. Test results show that the chloride permeability of concrete increases as w/c ratio increases whilst a limited amount of replacement of cement with silica fume, the chloride permeability decreases dramatically. The maximum aggregate size in the range of 8 to 25 mm seems also affect chloride permeability but with a much less significant level. The chloride permeability of silica fume lightweight aggregate concrete is very low, especially the concrete made with dry lightweight concrete. The chloride permeability can be evaluated by this accelerated test method.

Effect of Modification Treatment on Chloride Ions Permeability and Microstructure of Recycled Brick-mixed Aggregate Concrete

The modification methods of pozzolan slurry combined with sodium silicate and silicon-based additive were respectively adopted to treat recycled coarse brick-mixed aggregate(RCBA)in this study.The compressive strength and chloride permeability resistance of recycled aggregate concrete(RAC)before and after modification treatment were tested,and the microstructure of RAC was analyzed by mercury intrusion porosimetry(MIP)and scanning electron microscopy(SEM).The results show that the physical properties of RCBA strengthened by modification treatment are improved,and the compressive strength and chloride permeability resistance of treated RAC are also significantly improved.The modification treatment optimizes the pore size distribution of RAC,which increases the number of gel pores and transition pores,and decreases the number of capillary pores and macro pores.The surface fractal dimension shows a significant correlation with chloride diffusion coefficient,indicating that the variation of chloride permeability of treated RAC is consistent with the microstructure evolution.

Effect of Glass Powder on Chloride Ion Transport and Alkali-aggregate Reaction Expansion of Lightweight Aggregate Concrete

The effects of glass powder on the strength development, chloride permeability and potential alkali-aggregate reaction expansion of lightweight aggregate concrete were investigated. Ground blast furnace slag, coal fly ash and silica fume were used as reference materials. The re- placement of cement with 25% glass powder slightly decreases the strengthes at ？ and 28 d, but shows no effect on 90 d＇s. Silica fume is very effective in improving both the strength and chloride penetration resistance, while ground glass powder is much more effective than blast furnace slag and fly ash in improving chloride penetration resistance of the concrete. When expanded shale or clay is used as coarse aggregate, the concrete containing glass powder does not exhibit deleterious expansion even if alkali-reactive sand is used as fine aggregate of the concrete.

Effect of Ceramsite Structure on Microstructure of Interfacial Zone and Durability of Combined Aggregate Concrete

Structure characteristics of three kinds of ceramsite with different water absorption and the influence on microstructure of interfacial zone as well as performance of chloride permeabil-ity and frost resistance of combined aggregate concrete were investigated. The results show that, dense shell and closed internal pore have sharp effects on lowering water absorption of ceramsite. However, the ceramsite with high water absorption has obvious effect on the densification of interfa-cial paste which would develop a structure with lower porosity, finer aperture and higher microhard-ness. Furthermore, the impermeability and frost-resistance of concrete can be improved due to the ef-fect of water absorption and releasing by ceramsite with higher water absorption.

Experimental Research of Concrete with Steel Slag Powder and Zeolite Powder

In order to increase use ratio of steel slag solid waste,the concrete containing steel slag powder and zeolite powder as admixtures was prepared by using the orthogonal test method.The effects of water-binder ratio,sand ratio,steel slag powder content and zeolite powder on working properties,mechanical strength and chloride ion permeability of the concrete was studied.It was found that the early strength of the concrete had a decrease with the mixing of steel slag and zeolite powders,but its later strength approached to pure concrete.Moreover,the physical filling and pozzolanic activity of the admixtures increased the density of the concrete,resulting in the improvement of the durability of the concrete by the migration speed of Cl−reducing.The optimum mix ratio of C40 steel slag powder-zeolite powder concrete is obtained,and which had the slump of 220 mm,the 3 d,7 d and 28 d compressive strengths of 27.8 MPa,37.5 MPa and 48.4 MPa,the 6 h electric flux of 950 C and the diffusion coefficient of 1.65×10−12 m2/s.