Key Engineering Materials Vols. 405-406

Abstract: The crusher dust in Manufactured fine aggregate (MFA), e.g. limestone powder in calcareous MFA, constitutes micro gradation of the aggregate and suitable content of crusher dust in MFA can improve the properties of concretes. In this paper, early hydration processes of samples substituting limestone powder and fly ash for part of cement are analyzed, and effects of limestone powder on cement hydrates are studied through experiment of mortar prepared with MFA partially replaced by limestone powder and fly ash. The result reveals that both the dormant period and acceleration period of hydration ended earlier in the samples substituting limestone powder for part of cement, and amount of crystals of calcium hydroxide and hydrated calcium carboaluminate increases in hardened paste in the samples substituting limestone powder for part of MFA, i.e. calcareous dust (limestone powder) in MFA can stimulate and enhance hydration of cement.

Abstract: The hydration and expansive characterization of a novel concrete expansive agent were investigated in this paper. The results showed that the hydration activities of the novel agent depended on the calcining temperature, particle size and curing temperature. When the expansive agent was mixed in concrete, the early shrinkage of concrete was reduced. If the content and distribution of the expansive agent in concrete is appropriate and uniform, the expansion rate of concrete may be controlled, and the shrinkage of concrete could be compensated effectively by the gentle volume expansion.

Abstract: Concrete conductivity is the reflection of the micro pore structure and the pore solution conductivity of concrete, but the conductivity of pore solution changes considerably as different mineral admixtures are added, though the change is not always relevant to permeability and Cl- diffusivity. Saturation of concrete capillary pore system with 1 mol/l KOH solution through vacuum processing was tempted to maintain the pore solution conductivity constant, after which the concrete conductivity was a reflection of concrete porosity and tortuousity that closely related to Cl- diffusivity. Charge passed of concrete was also measured for comparison. It is shown that the conductivity of alkali saturated concrete without mineral admixtures was the biggest, followed by the concrete with natural zeolite（20％）, fly ash（30％）, slag（40％）metakaolin 20% and 10% of silica fume.

Abstract: Corrosion resistance coefficient of mortars incorporating different mineral admixtures were tested according to GB2420, and the expansion ratio of mortar bar immersed in 5% Na2SO4 solution was measured according to ASTM C1012. It is shown that all the mineral admixtures, including ground granulated blast furnace slag (SL) fly ash (FA), natural zeolite (NZ) and metakaolin (MK) were effective in decreasing the 15-week expansion and increasing the corrosion resistance coefficient of the specimens immersed in Na2SO4 solution as well.

Abstract: Charge passed of mortars with different aggregate volume fractions was tested according to ASTM C1202, and the differential expression of the Ohm law was introduced to explain the relationship between charge passed data and aggregate fractions.Cl- penetration depth of the corresponding mortars and concretes was measured to illustrate the influence of the aggregate volume fraction on their chloride permeability. It was shown that the charge passed of mortar was negatively correlated with aggregate volume fractions, and high aggregate fraction bearing concrete with low charge passed did not necessarily mean low permeability. As a result, the influence of aggregate fraction on charge passed should be taken into consideration when charge passed data was employed to evaluate Cl- permeability of concrete.

Abstract: The binding of sodium and potassium into cement paste influences the performance of concrete: for example, alkali balances between solid and paste constituents and pore fluid affect the potential for alkali aggregates reaction. However, quantification of the binding potential into paste solids has proven to be difficult, although much empirical data are available from pore fluid analyses. In this study, single-phase homogeneous C-S-H phases have been prepared at Ca: Si molar ratios (C/S) of 1.8, 1.6, 1.3, 1.0 and 0.8 and reacted with four alkali hydroxide concentrations, both NaOH and KOH, between 10 and 300 mM. A steady-state alkali partition is attained in less than 4d at 20°C by flame emission spectroscopy and the ξ potential of C-S-H and C-A-S-H gel unreacted and reacted with alkali hydroxide are measured. The results indicate：alkali binding into the C-S-H and C-A-S-H gel improves as its C/S decreases；Al3+ has been introduced to form C-A-S-H gels, and the influence of Al3+ on alkali sorption properties was determined: the replacement of Si4+ by Al3+ and Na+ or k+ markedly increases alkali binding and decreases the ξ potential of gel；the more Ca:Si ratio，the less alkali binding, the more ξ potential of gel.

Abstract: The chloride-resistant high performance concrete to be used is a basic technology to increase its durability in high chloride-ion environment. On the base of “Application technology guide for anti-seawater concrete of Guangdong province” (consultant version), the raw materials, mix proportion, placement of concrete, and the quality tests etc were discussed in detail.

Abstract: Permeation length, permeation coefficient of water permeated into concrete and chloride ion diffusion coefficient of C30, C45 and C60 concrete were studied by high hydraulic method (0.5MPa~25MPa) and quick method of testing chloride ion diffusion respectively, and relationship of concrete permeability tested by two methods was analyzed too. High hydraulic method can distinguish permeability of concrete with different strength or air content and it is a quick and effective method to fast test and evaluating permeability of concrete. The results showed that high hydraulic method is applicable for evaluating permeability of concrete, with advantages of short testing period, easy operating and simple pretreatment of concrete specimens. Permeation coefficient or permeation length of water permeated into concrete exhibited linear relationship with chloride ion diffusion coefficient of concrete. It is applicable for evaluating permeability of concrete using quick method of testing chloride ion diffusion.

Abstract: Concrete permeability has been an important part of durability assessment of existing structures. The preliminary application of in-situ permeation assessment by Autoclam system was reported in this paper. The reliability of this nondestructive method has been preliminary proved.

Abstract: The frost resistance of concrete subjected to 3.5% NaCl solution, 5%, 7%, and 10% Na2SO4 solution and seawater were investigated by quick freeze-thaw test. There were two criteria, the relative dynamic modulus of elasticity (RDME) and the mass of scaling, for evaluating the frost resistance of concrete. The results showed that scaling was the main characteristic of deterioration when concrete subjected to freeze-thaw cycles in 3.5% NaCl solution and seawater, whereas RDME had little change. When freezing and thawing in Na2SO4 solution, concrete failed because of internal damage and surfaces of lower strength concrete specimens appeared local swelling and scaling before failure. Concentration of Na2SO4 solution had influence on frost resistance of concrete: deterioration of concrete in 5% or 7% Na2SO4 solution was severe but slower when the concentration reached to 10%. Entraining air into concrete was the best method to improve the durability of concrete subjected to freeze-thaw cycles in all solutions.