Applied Mechanics and Materials Vols. 438-439

Abstract: As part of the studies on the durability of concrete with machine-made sand, this paper introduces the test results and the forecast model of time-dependent chloride penetration of this kind of concrete. Three strength grades of concrete C30, C40 and C50, and the contents of stone powder in machine-made sand of 5%, 9% and 13% in mass were considered in the mix proportion of concrete with machine-made sand. The ordinary concrete with natural river sand in the same strength grade was tested at the same time for comparison. The test was conducted for 360 days, the results showed that the effect of the content of stone powder on the chloride penetration of concrete was obvious at early curing time of 7 days, and tended to be lower with the increase of curing time. When the curing time was longer than 90 days, this effect could be neglected, and the resistance to chloride penetration of concrete with machine-made sand was almost equal to or larger than that of ordinary concrete. The decrement of chloride diffusion coefficient varied from sharp to gentle with the curing time, the resistance of concrete to chloride penetration increased with the increase of concrete strength. Meanwhile, to facilitate the calculation in practice, the forecast model of chloride diffusion coefficient of concrete is proposed.

Abstract: This paper introduces the experimental results of long-term carbonization of concrete with machine-made sand (MSC), which is part of the studies on durability of this new concrete. Three strength grades of concrete C30, C40 and C50, and the contents of stone powder in machine-made sand of 5%, 9% and 13% in mass were considered in the mix proportion of concrete with machine-made sand. The ordinary concrete with natural river sand in the same strength grade was tested at the same time for comparison. The test was conducted for 360 days, and the results showed that the carbonization of MSC was similar with that of ordinary concrete, the carbonized depth increased with the increasing carbonization time. The carbonization was rapid at initial before 28 days, and became slowly with the time going by. The content of stone powder in machine-made sand affected the carbonization of MSC in some extent, which should be limited in a reasonable range. Based on the test data, the formulas for forecasting the carbonized depth of MSC are suggested.

Abstract: Although the machine-made sand was widely used for concrete in recent years in China, it was short of studies on the relations among the basic mechanical properties of fly-ash concrete with machine-made sand (MSFAC). However, these relations such as the compressive strength, the tensile strength and the elastic modulus with the cubic compressive strength (i.e. strength grade) are the basis of design for concrete structures. This paper summarizes the test data from the published references, and discusses the relations among these properties by statistical analyses compared with those of ordinary concrete. The results show that only the tensile strength of MSFAC can be safely forecasted by the same formula of ordinary concrete specified in current Chinese design code. When the strength grade is higher than C45, the axial compressive strength of MSFAC is largely forecasted by the formula of ordinary concrete. The elastic modulus of MSFAC is larger than that of ordinary concrete, which should be prospect by the formula in this paper. This work gives out some cautions for the proper use of the MSFAC in concrete structures.

Abstract: To meet the requirement of machine-made sand application in concrete structures, it is necessary to understand the bond properties of steel bar with machine-made sand concrete (MSC). Therefore, the experimental studies were carried out on the bond of plain steel bar with MSC by the central pull-out test method. Three specimens were cast as one group, 6 groups were tested considering the changes of strength grade of MSC and ordinary concrete. The bond-slip curves were measured and analyzed. The results show that the bond slip begins at the tensile side and transfers gradually to the free end before the entire slip turns up along the interface of plain steel bar and surrounded concrete, the largest average bond stress, i. e. the bond strength of plain steel bar corresponds to the initial entire slip of plain steel bar. With the increasing strength grade of MSC and ordinary concrete, the difference of slip at tensile side and free end becomes greater. Comparing that only appears in ordinary concrete with higher strength, the larger slips turn up while the bond stress reaches the largest for the plain steel bar in MSC. Larger scatter of bond strength is between specimens in the same group. Some plain steel bars yields with the beginning of entire slip along the interface.

Abstract: Experiments were conducted to study sulfate attack on concrete made machine-made sand and fly ash (MSFAC). The cubes with dimensions of 100 mm were cast and immersed in sodium solution with sulfate-ion concentration of 50000mg/L and tested after exposed for 30, 90, 180, 270, 360 and 540 days. The powder samples were made by steps of drilling, cutting and grinding. The sulfate-ion contents of concrete at different depths were measured by the chemical titration method. The results show that the sulfate-ion content of concrete decreased with depth, the sulfate-ion entered concrete by diffusion, permeation and capillary absorption. The sulfate-ion content of concrete decreased with the increasing replacement of cement by fly ash, and also decreased with the increase of exposure time when 30% of cement is replaced by fly ash. There are some advantages of using fly ash for concrete with machine-made sand to resist sulfate attack.

Abstract: The Victoria State of Australia has the second largest reserves of brown coal on earth, representing approximately 20% of the worlds reserves, and at current use, could supply Victoria with its energy for over 500 years. Its combustion, annually, yields up to 1.3 million tonnes of fly ash, which is largely use for land-fills. Disposal of fly ash in open dumps cause massive environmental problems such as ground water contamination that may create various health problems. This study focuses on the usability of brown coal fly ash to develop a sustainable building material. A series of laboratory investigations was conducted using brown coal fly ash combined with cement and aggregate to prepare cold pressed samples aiming to test their properties. Initial results indicate that compressive strength satisfies minimum standard compressive strength required for bricks or mortar.

Abstract: Although the fly ash concrete with machine-made sand (MSFAC) was widely used in recent years in China, it was lack of studies on relations of compressive strength at different ages. According to the specification of Chinese standard, there are three ways of admixing fly ash (FA) into concrete, i.e. the additional admixing, the equal-mass replacing cement and the over-mass replacing cement. In this paper, 56 groups test data with additional admixing FA, 98 groups test data with equal-mass replacing cement and 86 groups test data with over-mass replacing cement for MSFAC are summarized from published references. Three linear formulas and Slatter formulas are fitted and compared for MSFAC by the different methods of admixing FA, all of them have good fitness with test data. The compressive strength at 28d can be predicted by the compressive strength at 7d with linear formula and Slatter formula for MSFAC.

Abstract: In this work the adsorption of phosphate using the Fe-Cu bimetal oxide modified fly ash was studied. The experimental results showed that phosphate could be effectively removed in the pH range between 4 and 10. The removal percentage of phosphate reached maximum at pH 6.0. The adsorption of phosphate by the modified fly ash was rapid, and the adsorption percentage of phosphate could reach 91.20% in 5 minutes. The removal efficiency of phosphate increased with the increase of adsorbent dosage and the decrease of the initial concentration. The adsorption of phosphate could be described well by Langmuir isotherm, the Langmuir constant Q₀ was 26.03mg/g.

Abstract: The test and contrast mortars were made by changing water-binder (water-cement) ratio from 0.4 to 0.6, fly ash replacing rate from 10% to 30% and over-mass factor of fly ash from 1.3 to 1.7 with different methods of equal-replacing and over-mass replacing cement by fly ash. The variation of compressive and flexural strengths of mortar with water-binder ratio and admixing amount of fly ash are analyzed based on the test strengths. The formulas for calculating active factor of fly ash are proposed, and the regularity of active factor with the change of water-binder ratio and admixing amount of fly ash are given out.