Advanced Materials Research Vols. 671-674

Abstract: The pore structure in intact and inelastically deformed Indiana limestone have been studied using x-ray microtomography imaging. Guided by detailed microstructural observations and using Multi-level Otsu’s thresholding method, the 3D images acquired at voxel side length of 4 μm were segmented into three domains: solid grains, macropores and an intermediate zone dominated by microporosity. Local Porosity can be defined to infer the porosity of each voxel. The macropores were individually identified by morphological processing and their shape quantified by their sphericity and equivalent diameter. With this segmentation, we obtained statistics on macropores on intact and deformed Indiana limestone which shows that inelastic compaction was followed by a significant reduction in the number of macropores. And also our results revealed the great potentiality to produce a quantitative analysis on porous material with the aid of micro CT images.

Abstract: Under summer climatic features of Daqing area in China, numerical simulation on the unsteady heat transfer characteristic of phase change roof was investigated, considering direct influence of solar radiation. The main influencing factor of roof slope in the phase change roof was analyzed in this paper. The results show that, increasing the roof slope is beneficial to promote the effect of heat-insulating and temperature-reducing of phase change roof, whereas the extent of the ascension is weak. Different slopes in roof structure have basically no influence on the delay effect.

Abstract: Several compound mineral admixtures, such as steel slag powder, granulated blast furnace slag powder and silica fume, are mixed with proper proportion to improve the workability of High Performance Concrete（HPC）. Through the orthogonal experiment, workability of HPC is analyzed on water-binder ratio, sand ratio, the amount of superplasticizer and the amount of compound mineral admixtures. Results show that: workability of HPC was significantly effected by the amount of naphthalene sulphonate water-reducing admixture and water-binder ratio, the amount of compound mineral admixtures and sand ratio are impact factors on the workability in a certain extent.

Abstract: In order to have a better understanding the wearability of bamboo pulp fabric and enhance the research and development level of this kind of products, the fabric performances such as the strength, elongation, air permeability, moisture permeability have been test and discussed in this paper. The results shown that: the breaking strength of fabric increases when the bamboo pulp fiber content reduces; when the bamboo pulp fiber content increased, the breaking elongation, wear resistance performance, wicking performance, crease recovery performance, moisture permeability, air permeation rate and tearing strength of fabric also increased.

Abstract: A new green building material has been studied through investigating the thermal insulation properties of board produced from crop straw in this paper. Three straw-based boards with different thicknesses (8mm, 16mm and 32mm) were selected to detect heat transfer coefficient of the wall using JW-III heat-flow meter type thermal conductivity tester. Based on the standard specified in [1], we obtained the minimum thickness for the straw-based board for thermal insulation of different thickness brick walls.

Abstract: The experimental investigation of the preparation process of recycled aggregate concrete (RAC) using the waste concrete as recycled aggregate concrete (RCA) was reported. By conducting a series of laboratory experiments, the crushing and sieving procedure of wasted concrete to produce RCA were studied, the RACs with different strengths were designed, the strengths of hardened concrete were investigated. The results indicated that the representative strength for designing C10, C15 and C25 grade RAC using RCA were 11.3, 16.2 and 27.3 Mpa, respectively. The results gained in this study prove to be a valuable building materials using RCA for doveloping the RAC. Recycling and reuse of building wastes have been found to be an appropriate solution to the problems of dumping hundred of thousands tons of debris accompanied with shortage of natural aggregates.

Abstract: Two iron mine tailing sands and manufactured sands with different fineness modulus are studied and they are mixed into four mixed sands which fineness modulus is 2.6~3.0 by controlling mixing amount of iron mine tailing sand. The influence of mixed sands on workability and strength of C30 and C50 concrete are studied. The result shows that C30 and C50 concrete slump can reach 170mm. Concrete workability is good and strength is qualified too. Fineness modulus is the most important performance index when iron mine tailing sand is used in concrete.

Abstract: It is well established that external confinement of concrete with fiber reinforced polymer (FRP) sheets results in significant improvements on the axial compressive behavior of concrete. This understanding has led to a large number of experimental studies being conducted over the last two decades. However, the majority of these studies have focused on normal strength concretes (NSC) with compressive strengths lower than 55 MPa, and studies on higher strength concretes have been very limited. This paper presents the results of an experimental study on the compressive behavior of FRP confined high- and ultra high-strength concrete (HSC and UHSC) with average compressive strengths of 65 and 100 MPa. A total of 29 specimens were tested under axial compression to investigate the influence of key parameters such as concrete strength and method of confinement. All specimens were cylindrical, confined with carbon FRP and were 305 mm in height and 152 mm in diameter. Results obtained from the laboratory testing were graphically presented in the form of axial stress-strain relationships and key experimental outcomes are discussed. The results of this experimental study indicate that above a certain confinement threshold, FRP-confined HSC and UHSC exhibit highly ductile behavior. The results also indicate that FRP-wrapped specimens perform similar to concrete-filled FRP tube (CFFT) specimens at ultimate condition, however notable differences are evident at the transition region when comparing stress-strain curves.

Abstract: It is widely considered that crushed construction aggregate waste creates a lower compressive strength kind of concrete. This paper presents experimental investigation on axial compression strength of 18 recycled aggregate concrete cubes under the freeze-thaw test. The research has focused on the effect of the freezing-thawing test on the ultimate carrying capacity of recycled concrete cubes with different coarse aggregate replacement ratio. This study confirms that freezing-thawing cycles have a greater effect on the ultimate bearing capacity of recycled concrete cubes. Some measures should be taken to prevent the recycle concrete from the freeze-thaw damage, for example add air entraining agent to concrete.

Abstract: Basalt fiber (BF) has a lot of advantageous properties. The actual effectiveness of the fiber depends greatly on their dispersion degree in the composites. With the help of ultrasonic wave and a dispersant carboxymethyl cellulose (CMC), the even dispersion of short basalt fibers in water is realized. The fluidity of the basalt fiber cement mortar becomes less as the fiber content increasing. When the fluidity of mortar of BFRC is greater than 170mm, the even dispersion of short basalt fibers in BFRC can be realized. Fly ash can effectively improve the fluidity of BFRC and the density of cement matrix. When the amount of fly ash replaces the cement less than 25% by weight, it can improve both the compressive strength and tensile strength at age of 28 days.