Papers by Author: Feng Xing

Abstract: Self-healing concrete is a kind of smart concrete, and becoming one of research focus both in material and civil engineering field, in the paper, main self-healing methods concluded and partial technical problems of the self-healing facing, aim to these problems designed a kind of novel self-healing system, and experimental analyzed mechanism of self-healing.

Abstract: Base on engineering application need, the subject introduce microcapsule that contains adhesive into cementituous composite for realizing the self-healing characteristics of cracked concrete. The technique has good industry feasibility, process operability, and reproducibility of self-healing characteristic. It is can resolve partial problems that other current self-healing methods are facing.

Abstract: Crack will occurs when concrete structure under external load, temperature change, the crack may reduce the service life of concrete structure, to the macrocrack, there are many mature repair method, but microcrack is difficult to detect and repair. Self-healing techniques provide reliable and effective choice to microcrack repair. The paper reviewed the development of self-healing techniques, and analyzed the prospect of this field.

Abstract: Phosphoaluminate cement (PAC) sets quickly and develops high early strength. As a novel cementitious material, its hydration mechanism and microstructure are more complex than ordinary cement. Based on nitrogen adsorption isotherm method, investigated characteristic of adsorption isotherm of PAC paste, adsorption loop and pore distribution at different hydration period with various W/C ratio, results show that adsorption and desorption isotherm are tight relate to pore structure and pore distribution. In addition, the study analyzed the scope of application of nitrogen adsorption isotherm method on investigating pore structure of cement paste.

Abstract: Electrodeless resistivity and impedance spectroscopy measurement are reliable equipments of test online for monitoring the hydration process of cement-based materials continuously and accurately. Phosphoaluminate cement (PAC) sets quickly and develops high early strength. In order to understand the mechanism, the hydration products and microstructure formation of PAC in early age need to be studied. In the study, early hydration process and impedance spectroscopy characteristics of PAC with different dosage of retarder were investigated. According to the test, resistivity of freshly mixed PAC paste decreases sharply and then rises slowly, some characteristic peaks appear at different hydration stages of PAC, which indicates the hydration process of PAC includes four stages which are dissolution, induction, acceleration and deceleration. Impedance spectroscopy can reflect the change of micro-structure and ion concentribution of PAC matrix by resistance and capacitance.

Abstract: The paper studied effect of blast-furnace slag on rheology and hydration properties of blended cement paste. Rheology of blended cement paste with polycarboxylic series (PCS) and sulphamate series (SMS) superplasticizer is tested, appraised effect degree of the dosage and fineness of slag in blended cement by saturation dosage of superplasticizer, fluidity and gradual loss of fluidity. For hardened paste, the study tested development of strength and hydration products, activation effects of gypsum and sodium sulfate, analyzed macro mechanical behavior and micro structure of blend cement made from slag.

Abstract: Mechanical behavior of sulphoaluminate cement (SAC) mortar mixed slag (SL), fly ash (FA) and combined admixture were studied in the study, at the same time, hydration products and micro-structure were analyzed with XRD and SEM for making clear hydration mechanism. Test results show that early period strength of SAC mortar decreased, and strength contribution rate of admixture is combined admixture (slag + fly ash) ＞ slag ＞ fly ash on the same content due to the combined admixture is more beneficial to accelerate hydration. Yet strength increase of SAC mortar mixed admixture after cured 60d is not obvious, which was not large different with pure SAC mortar. A large amount of ettringite and gel produced during 1d period of SAC paste, but with the hydration carrying on, diffraction peak of hydration products (ettringite and gel) and unhydrated calcium sulphoaluminate change little, which means hydration degree at 1d is higher. Diffraction peak of ettringite and gel at different curing period is lower when mixed admixture in matrix, the amount of ettringite and gel increased and unhydrated calcium sulphoaluminate decreased with hydration carrying on, which means early hydration speed slow down when introduction of admixture into SAC matrix.

Abstract: Many investigations have been conducted on compressive strength of lightweight aggregate concretes (LWAC), but there are few experimental studies on the relationship between compressive strength, bond strength and elastic modulus of LWAC. In this paper, the specimens of twenty kinds of LWACs with different mix proportions were made. Properties of compressive strength, bond strength and modulus of elasticity of the LWACs were tested. Based on the testing resulting, equations for relationship between bond strength and compressive strength of the LWAC were established. For LWAC modulus of elasticity, the experimental results of this study can fit well with predicted equation of ACI 318

Abstract: Penetration and diffusion of chloride ions in concrete can lead to the corrosion of steel bar and shorten the service life of concrete structures. Phosphoaluminate cement (PAC) is a new cementitious material which has many special properties compared to Portland cement (PC). In the study, chloride ion diffusion in PAC concrete was tested with RCM method. The phase composition and morphology of hydration products, pore volume of hardened paste cured for 28d were analyzed with X-ray diffraction (XRD) and mercury intrusion porosimetry (MIP). The results show that chloride ion diffusion coefficient of PAC concrete is much lower than that of Portland cement concrete under the same test conditions. The hydration products of PAC are main micro-crystalline phase and gel of phosphate and/or phophoaluminate, which formed a dense microstructure. There is no calcium hydroxide produced in the PAC hydration system. In hardened PAC paste, chloride ions might replace the atom group [OH] - and [PO4]3- of hydrates and become stable compounds. The resistance to chloride ion diffusion of PAC concrete will increase with the hydration age, because its microstructure becomes denser with the hydration age increasing.

Abstract: An electrodeless resistivity measurement system developed recently can provide a reliable method for monitoring the hydration process of cement-based materials continuously and accurately. Phosphoaluminate cement (PAC) sets quickly and develops high early strength. In order to understand the mechanism, the hydration products and microstructure formation of PAC in early age need to be studied. In the study, early hydration process of PAC with different dosage of retarder was investigated by the electrodeless resistivity equipment. According to resistivity-time curve, resistivity of freshly mixed PAC paste decreases sharply and then rises slowly, some characteristic peaks appear at different hydration stages of PAC. Heat evolution of PAC was also measured. The hydration mechanism and structure formation were studied according to these results. Depending on the dosage of retarder, the hydration process of PAC includes four stages which are dissolution, induction, acceleration and deceleration.