Hu Shuguang

Research on the hydration, hardening mechanism, and microstructure of high performance expansive concrete

High performance expansive fly ash concrete (HPEC) was prepared and the differences of mechanical properties between the high performance concrete and HPEC were compared under free- and confined-curing conditions. By means of XRD and SEM methods, the hydration progress and microstructure of HPEC were investigated. The results show that an expansive agent is useful and the confinement action could improve the microstructure of hardened expansive concrete.

Effect of fine steel slag powder on the early hydration process of portland cement

Hydration heat evolution, non-evaporative water, setting time and SEM tests were performed to investigate the effect of fine steel slag powder on the hydration process of Portland cement and its mechanism. The results show that the effect of fine steel slag powder on the hydration process of Portland cement is closely related to its chemical composition, mineral phases, fineness, etc. Fine steel slag powder retards the hydration of portland cement at early age. The major reason for this phenomenon is the relative high content of MgO, MnO2, P2 O5 in steel slag, and MgO solid solved in C3 S contained in steel slag.

Effect of pre-wetted light-weight aggregate on internal relative humidity and autogenous shrinkage of concrete

This research indicates that the gradient of internal relative humidity (IRH) decreases rapidly within 1-day curing age in HPC. The amount of water imported by pre-wetted light-weight aggregate can regulate IRH of concrete. By importing a proper amount of water, the process of the decline of IRH can be delayed and the autogenous shrinkage can be reduced. The relationship among the amount of water imported by pre-wetted lightweight aggregate, IRH and AS was established. The result provides a new method of reducing early AS and enhancing early cracking resistance of HPC.

Research on Alkaline Filler Flame-Retarded Asphalt Pavement

Used as flame retardant of tunnel asphalt pavement, organic bromides produce a large amount of poisons and smoke in construction and flame retardation stage. The alkaline filler was found to replace mineral filler, and the flame-retarded asphalt mixtures were produced. Experimental results show that these asphalt mixtures are smoke restrained; the performances and construction technology of asphalt pavement are not influenced; also the alkaline filler is of low-price. So this kind of flame-retarded asphalt mixtures is suitable for tunnel pavement.

The microstructure of the interfacial transition zone between steel and cement paste

Abstract The microstructures of steel/ordinary paste and steel/expansive paste interfaces were investigated. The Ca(OH) 2 orientation effect, the crystal sizes of Ca(OH) 2 and AFt, the morphologies and the relative percentages of the Si, Al, S and Ca elements of interfaces were specially studied. The results show that, under confined conditions, the microstructure of the steel/expansive paste interface is better than that of the steel/ordinary paste interface.

Influence of mineral admixtures on the permeability of lightweight aggregate concrete

The permeability of lightweight aggregate concrete was studied. Some efforts were taken to increase the resistance of lightweight aggregate concrete (LC) to water penetration by using the mineral admixtures of fly ash, granulated blast furnace slag or silica fume. Accelerated chloride penetrability test and liquid atmosphere press method were used to study the anti-permeability of lightweight aggregate concrete. The experimental results show that fly ash, granulated blast furnace slag and silica fune can decrease the permeability of lightweight aggregate concrete, but the effect of granulated blast furnace slag is poor. According to the SEM and pore structure analyzing results, an interface self-reinforcing effect model was presented and the reinforced mechanism of mineral mixture on LC was discussed according to the model described by authors.

Autogenous Shrinkage of High Strength Lightweight Aggregate Concrete

The characteristic of autogenous shrinkage (AS) and its effect on high strength lightweight aggregate concrete (HSIAC) were studied. The experimental results show that the main shrinkage of high strength concrete is AS and the amount of cement can affect the AS of HSLAC remarkably. At the early stage the AS of HSIAC is lower than that of high strength normal concrete, but it has a large growth at the later stage. The AS of high strength normal concrete becomes stable at 90 d age, but HSIAC still has a high AS growth. It is found that adjusting the volume rate of lightweight aggregate, mixing with a proper dosage of fly ash and raising the water saturation degree of lightweight aggregate can markedly reduce the AS rate of HSIAC.

The hydration of blended cement at lowW/B ratio

The hydration process, hydration product and hydration heat of blended cement paste mixed with mineral admixture and expansive agent at low W/B ratio are studied by XRD, thermo analysis, and calorimetry instrument, and they were compared with those of pure cement paste. The results show that pure cement and blended cement at low W/B ratio have the same types of hydration products, but their respective amounts of hydration products of various blended cements at same ages and the variation law of the amount of same hydration products with ages are different; The joint effect of tumefaction of gel-ettringite due to water absorption and the expansive pressure on the pore and rift caused by the crystalloid ettringite is the impetus of the volume expansion of cement paste, and the former effect is much greater than the latter one.

Performances of the High Strength Low Heat Pump Concrete (HLPC)

The effects of mineral admixtures on fluidity, mechanical and hydrational exothermic behavior were studied. The results show that, double-adding ways, i e, fly ash and slag were added at the same time, not only improves the fluidity of fresh concrete with low W/B and compensates the lower early compressive strength of harden concrete caused by high adding amount of fly ash, but also greatly reduces the highest temperature rise, exothermic rate and total heat liberation of 3 day of binder pastes in HLPC, and postponed the arrival time of the highest temperature rise. HLPC was prepared and applied to project practice successfully.

XPS nondestructive depth analysis method and its application in cement based composite materials

Abstract This paper introduces the principle and testing method of X-ray photoelectron spectroscopy (XPS) angle variation technique which is a nondestructive surface depth method and compares it with the mechanical stripping method and the ion etching method. Thereby, the depth analysis of the composite interfacial layer between polyacrylamide and monocalcium aluminate in MDF cement has been carried out. The chemical reaction mechanism and the structural properties have also been discussed in light of the experimental results.