Materials Science Forum Vol. 1036

Abstract: To explore the effect of mechanical activation on the particle size distribution of the composite admixture a self-designed test jet mill is used. We have studied the effects of different specific surface areas of composite admixtures on the workability, mechanical properties and durability of concrete and combined X-ray diffraction (XRD) with scanning electron microscopy (SEM) to analyze the mechanism of concrete performance improvement. Results showed that, mechanical activation can significantly increase the content of particles below 3 um; appropriate increase in the specific surface area of composite admixture is conducive to improving the performance of concrete; As the specific surface area increases, the hydration activity of the composite admixture increases first and then tends to be stable; during the hydration process, more thin-plate Ca(OH)₂ is converted into needle-shaped AFt, which improves the cement-based material and thereby improving the macro mechanical properties and durability.

Abstract: Adding sap particle, Portland cement foamed concrete was studied to manufacture a new type of planting material. The pH, porosity, permeable capacity, infiltration rate and water storage were tested for evaluating the performance of foamed concrete. Solid-liquid extraction method and image binaryzation were used to study the pH and porosity of foamed concrete. A kind of self-made permeable device was also used in this paper. It was found that the pH of foamed concrete could be decreased by sap particles absorbed the boric acid solution in 14 d. For the foaming effect of fresh concrete was disturbed by liquid from sap particles, the porosity of foamed concrete was increased and then decreased. Seepage channels could be formed in foamed concrete when sap particles shrunk for releasing liquid and they also would be block for sap particles expanding when water permeated into foamed concrete. The permeable capacity and infiltration rate were decreased with increasing sap particles. The water storage of foamed concrete was fluctuated with sap particles increasing but more than that without sap particles. The optimal dosage of sap particles was 0.3wt% of binder material in this study. At the dosage, the minimal pH of foamed concrete could be obtained and performance of that would be good to plant, such as permeable capacity, infiltration rate and water storage.

Abstract: Large inventory and non-degradability made waste glass fiber reinforced plastics (GFRP) a heavy burden to environment. They are increasingly reclaimed through mechanical crushing and used as aggregate replacement in concrete. However, reuse of all-component recycled GFRP (rGFRP) was still limited due to the inconsistent influences of powder and fiber on cementitious materials. In this study, mortar and concrete with two different gradations of all-component rGFRP at 10 wt%, 20 wt% and 30 wt% were investigated with mechanical tests, ultrasonic pulse velocity inspection, Depth-of-Field optical microscopy, Scanning Electron Microscopy (SEM) and micro-CT. It revealed that the splitting strength of cement mortar was significantly increased while 10 wt% of rGFRP was added, whereas the compressive and flexural strength were barely affected. For concrete, the initial and final setting time were prolonged by the addition of 30 wt% rGFRP up to 93.8% and 124.3%, respectively. The mechanical strength of concrete increased with rGFRP content firstly, and then decreased, due to the reduced dispersity of rGFRP and compactness of mortar. When 10 wt% of rGFRP was added, the 28-day compressive, flexural and splitting strength of concrete were optimized to 25.8 MPa, 4.25 MPa and 3.02 MPa, respectively. The failure pattern analysis indicated that rGFRP can restrain crack propagation, reduce crack width and improve the integrity of fractured concrete. The results suggested the potential feasibility of rGFRP as fine aggregate replacement, and provided solid experimental references for practically reusing rGFRP in cementitious materials.

Abstract: Replacing cement and silica fume with glass powder to prepare ultra-high performance concrete (UHPC) is beneficial to solve the ecological problem in the field of civil engineering, but the technologies of preparation, transportation, pumping, and hardening of UHPC mainly relate to its rheological property. Therefore, this paper studied the influence of glass powder on the rheological properties of UHPC paste by performing the flow and the rheological test. Experimental results showed that when the cement and silica fume partially replaced by glass powder, the UHPC paste appears shear thickening, yield stress, plastic viscosity, and area of hysteresis loop decrease. This means that mixing glass powder can somehow inhibit the problems of segregation and bleeding of UHPC during pumping. In this manner, the dosage of the superplasticizer in UHPC is appropriately reduced, the filling capacity of UHPC during pouring is improved, and the energy required for UHPC in the pumping process is weakened. Compared with replacing cement, replacing silica fume with glass powder significantly increases the shear thickening and fluidity of UHPC paste, and at the same, reduces its yield stress and plastic viscosity. This indicates that the construction performance of UHPC is greatly improved with the replacement of silica fume. The fluidity and yield stress of UHPC paste satisfy the quadratic polynomial function relationship, and the replacement of cement and silica fume with glass powder should be less than 33% and 50%, respectively. Under this condition, the rheological properties of the UHPC paste are greatly improved and result in little negative impact on the mechanical properties of UHPC.

Abstract: The ITZ (interfacial transition zone) in concrete has very high porosity and permeability, which affects concrete’s macroscopic mechanical properties and transport properties. Two-dimensional (2D) areal analysis and one-dimensional (1D) linear analysis are usually used to study ITZ’s microstructure. However, 3D microstructure is difficult to be characterized by 1D and 2D information. For example, 2D cross-section planes do not always intercept both the ITZ and the corresponding aggregate, which causes some ITZ regions are ignored by researchers. Therefore, ITZ’s volume and thickness will be misestimated, and leads to the misestimation of the diffusivity. In this paper, the effect of aggregate’s shape on the misestimation of ITZ thickness t is studied. The results reveal that the misestimation increases with the increasing sphericity s of aggregates.

Abstract: The external surface of the building envelope absorbs large amounts of heat after long periods of solar radiation especially in the hot summer, leading to a dramatic increase in the cooling load and energy consumption. Phase change material (PCM) possesses the ability to reduce building energy consumption and improve thermal comfort when it is integrated with the building envelope. In this study, paraffin /expanded graphite (EG) composite phase change material was prepared to fabricate facing tile for building envelopes, with phase change facing tile (PCMT) attached to exterior walls and roofs. To present the full role played by the paraffin/ expanded graphite composite phase change material, microstructure, thermal and physical properties characteristics were investigated, thermal performance experiment of facing tile was carried out. The results showed that the maximum inner surface temperature difference between the PCMT and the ceramic tile reached 2.5°C, the maximum temperature time lag was 51 min. A simulation in EnergyPlus was used to evaluate the availability of using PCM to improve the energy efficiency of the building under the Guangzhou climate. The results showed that 2.65% energy savings were achieved. These results showed that PCM has thermal insulation performance, which would affect the indoor temperature and reduce building energy consumption to some extent.

Abstract: A styrene-butadiene-styrene triblock copolymer (SBS) was grafted with an unsaturated polar monomer (monomer A) composed of maleic anhydride (MAH) and methoxy polyethylene (MPEG) via a ring-opening reaction after epoxidizing styrene-butadiene-styrene triblock copolymer (ESBS). The microscopic changes of SBS before and after grafting has been characterized with Fourier transform infrared spectrum (FT-IR), X-ray photoelectron spectroscopy (XPS) and gel permeation chromatography (GPC). The results revealed that the monomer A was successfully grafted on SBS backbone, and the maximum graft ratio (GR) was 20.32%. To verify the compatibility between SBS and asphalt, solubility parameters and surface free energy (SFE) of SBS, grafted SBS and asphalt were measured. It was found that the solubility parameter and SFE of grafted SBS were closer to asphalt compared with SBS. It also has been confirmed from storage stability that the temperature susceptibility of grafted SBS modified asphalt was reduced in compare with SBS modified asphalt binder. As consequence, the use of grafted copolymer can be considered a suitable alternative for modification of asphalt binder in pavement.