Papers by Author: Chang Yong Li

Abstract: On the basis of experimental results, this paper discusses the shear-crack behaviors such as shear-cracking force and shear-crack width of reinforced full-recycled aggregate concrete beams. The full-recycled aggregate concrete was developed for the sustainable development in civil engineering, in which the coarse aggregate was the recycled aggregate made of abandoned concrete, and the fine aggregate was the machine-made sand. Sixteen beams, six of them without stirrups, were tested with the shear-span ratio varying as 1.5, 2.0 and 3.0, and the ratio of stirrups varying from 0.19% to 0.35%. The results showed that the shear-cracking force of the beam was mainly affected by the shear-span ratio, the width of shear-cracks intersecting stirrups decreased with the increasing ratio of stirrups, but the maximum crack width almost exceeded the limit 0.3mm in the first class environmental condition specified in Chinese code GB50010-2010. Comparing the calculation results by substituting the test parameters of full-recycled aggregate concrete beams into the formula of ordinary reinforced concrete beams, the lower resistance of reinforced recycled concrete beam to shear-cracking, and the larger crack width intersecting stirrups should be noted in the structural design. Based on the test data, the formula for calculating the shear-cracking force and the shear-crack width of reinforced full-recycled aggregate concrete beams are suggested.

Abstract: To improve the flexural properties and lighten the weight of ordinary reinforced concrete beam (RCB), this paper develops a new type of superposed RCB in which the tensile zone was partially cast with the steel fiber reinforced full-lightweight concrete (SFRFLC). 10 beams with different height of SFRFLC were designed. Their flexural behaviors were measured including the concrete strain at mid-span cross section, the load vs deflection curve, the cracking load and the ultimate load. It may be concluded that the test beams damage in ductile, the concrete strains at mid-span cross section basically fit the assumption of plain cross section, the variations of load vs deflection curves are similar with obvious changes at the points of the cracking of concrete and the yield of tensile reinforcements, the cracking loads are almost equal, and the ultimate loads tends to decrease with the increasing height of SFRFLC. The SFRFLC and ordinary concrete work well together, the suitable height of SFRFLC is there should be further studied.

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: This paper introduces the test results of eight steel fiber reinforced lightweight aggregate concrete (SFRLAC) superposed two-way slabs under punching load. The tensile and compressive zones of the slabs were cast with the SFRLAC and the ordinary concrete respectively. The slab was simply supported along the four edges under central concentrated load on the short column. The main parameter of SFRLAC was the fraction of steel fiber by volume of 0.8%, 1.2% and 1.6%. The measurements were made such as the deflection, the strains of steel bar and concrete, the crack distribution, the loads corresponding to the yielding of steel bar and the ultimate state. It proved that the punching resistance of SFRLAC superposed two-way slab increased about 51%~78% with the increasing fraction of steel fiber by volume, the ability to resist punching deformation was enhanced remarkably, many fine cracks distributed on the tensile surface, and the ductility at failure state increased to a certain degree.

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.

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: Compared with ordinay concrete, weight of lightweight aggregate concrete could be lower 20%-40% under same bearing capacity. Mixed with some given steel fibers in it, crack resistance and flexural strength will be improved. Once lightweight aggregate concrete mixed with steel fibers meets the requirements of frost resistance, it could be applied to most civil engineerings in a cold area. In this paper, the frost resistance mechanism of steel fiber reinforced lightweight aggregate concrete is introduced. The research status of frost resistance of steel fiber reinforced lightweight aggregate concrete is reviewed including the effects of water cement ratio, aggregate, mineral admixture and amount of fiber, frost resistance experimatal methods and engineering applications etc. Some further researches are prospected.

Abstract: This paper introduces the test results of the flexural performance of CF40 steel fiber reinforced concrete (SFRC) designed by the binary superposition mix design method. The flexural strength and flexural load ~ deflection curves were got from the test SFRC specimens with the different fraction of steel fiber by volume and the different thickness of cement paste wrapping steel fibers. The effects of the fraction of steel fiber by volume and the thickness of cement paste on the flexural strength and toughness of SFRC are analyzed. It is demonstrated that the flexural toughness of SFRC increases with the increase of the fraction of steel fiber by volume, the reasonable thickness of cement paste wrapping steel fibers is 1.0mm.

Abstract: To meet the requirement of machine-made sand application in concrete structures, experimental studies were carried out on the bond of plain steel bar with Machine-made Sand Concrete (MSC) by the central pull-out test method. Three specimens were cast as one group, 14 groups were tested considering the influence of concrete strength, bond length and stone powder content in machine-made sand. Based on the experimental research, the characteristic values of bond-slip curve such as the initial-slip and ultimate bond stresses with corresponding slips are statistically analyzed, the bond-slip constitutive relations between plain steel bar and MSC were obtained.

Abstract: Due to many different characteristics such as irregular polygon particle with pointed edges, rough surface and larger content of stone powder, machine-made sand has ignorable effects on the properties of concrete. As the basis for the design of concrete structures, the relations among the basic mechanical properties of concrete such as compressive strength, tensile strength, flexural strength and elastic modulus should be clearly understood. 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 the axial compressive strength and the tensile strength can be prospected by the same formulas of ordinary concrete specified in current Chinese design code, but the prospected tensile strength should multiply a reducing coefficient when the strength grade of concrete is lower than C30. The elastic modulus of concrete with machine-made sand is larger than that of ordinary concrete, which should be prospect by the formula in this paper. Meanwhile, the formula of flexural strength is suggested.