Key Engineering Materials Vol. 509

Abstract: In this paper, the construction and demolition waste (C&D waste) recycling techniques in China is summarized, and proposed the C&D waste recycling suggestions in this foundation. The C&D waste can be divided into construction waste, decorating waste, demolition waste and natural disaster ruin waste. In addition to be buried, domestic C&D waste can be made into landscape material, roadbed material, recycled aggregate, recycled brick, recycled concrete, recycled admixture and so on. The state should establish positive promoting policies, improve the recycling industrial chain, and promote the healthy development of the C&D waste recycling.

Abstract: The effect of mineral admixture and curing condition in pore structure of concrete was studied in this paper. Concrete samples with different component were prepared firstly, and then they were put into standard condition, fresh water and salt environment that produced artificially respectively at 20 °C. After the experiments of curing at 3, 28 and 180 days pore structure were tested by mercury intrusion porosimetry (MIP). The results obtained reveal that with the increase of the age, the pore structure degradation impact in salt environment of concrete increase dramatically. When at 28 days, total pore volume and porosity of concretes in fresh water is lower by 20% and 5% respectively than the ones with larger mean pore size and critical aperture in salt environment, which represents pore refinement in fresh water had a good effect. Compared to the salt environment erosion, it can be found that the impact of pore refinement in fresh water is more significant.

Abstract: By using XRD、SEM and other experimental methods, some details of polycarboxylate superplasticizer on the hydration products and performance of phosphogypsum-based cement(PBC) can be obtained. It can be found that the polycarboxylate superplasticizer makes the structure of the cement stone more compact, and significantly increases the strength of the cement. Besides, it can also improve the anti-carbonation and degradation properties of that cement.

Abstract: Gypsum is an indispensable component of ordinary Portland cement. The main function of gypsum is to regulate the setting time of cement. Gypsum has a great influence on water consumption of standard consistence and strength simultaneously. In this article three cementitious systems are prepared by three main mixed materials: limestone, fly ash and slag. The effect of gypsum content and the relation between gypsum quantity and the fluidity of cement with Marsh cone method are studied. Experimental results show that when the gypsum was added in the three kinds of cementitious system, water consumption of standard consistence decreased obviously, and with the quantity of gypsum increased, water demand for normal consistency reduced first, up to a certain extent tended smoothly. With the increase of gypsum quantity, initial and final setting time had different degrees of extension. While a saturation quantity is achieved, setting time will keep steady. The flexural strength and the compressive strength increased gradually and tended to be stable with the increase of gypsum quantity. When gypsum content exceeded a certain range, compressive and flexural strength decreased gradually. But gypsum content and the mobility of systems had little relativity with Marsh cone method.

Abstract: Semi-flexible pavement (SFP) has some excellent characteristic such as high carrying capacity, good wearing resistance, water stability and durability. However, the SFP appears low temperature crack and fatigue cracking seriously because there are large differences in the interfacial bonding property and the elastic modules between its two major parts: Lag gap asphalt mixture (LGAM) and cement mortar. All of these are caused by the large stiffness of cement mortar. In order to improve the crack resistance property of SFP, six kinds of cement-emulsified asphalt mortars (CEAM) were developed to enhance the adhesive property and reduce the elastic modules. The cement-emulsified asphalt mortar semi-flexible pavement material (CEAMSFP) was obtained by using this kind of CEAM. In the CEAM and the CEAMSFP, six emulsified asphalt-to-cement (A/C) ratios were considered in the study: 0, 0.1, 0.2, 0.3, 0.4 and 0.5 by weight of emulsified asphalt. The results indicated that the increasing of the A/C ratio improved the bonding interface and the flexible of the CEAM. The increasing of the A/C ratio improved the low temperature resistance and fatigue life of the CEAMSFP. It was also shown that the A/C ratio of 0.3 was found to be the optimum ratio that achieved a balance in performance and the value of the pavement. In this condition, the adhesion level between LGAM and cement grout reached 5，the elastic modules of mortar decreased by 62.5% and the fatigue life of SFP increased by 43.6%.

Abstract: Concrete with a compressive strength of 100MPa was produced with metakaolin(MK), and the effect of MK replacement levels on compressive strength of concrete with a water to binder ratio of 0.25 was studied in this paper. XRD, microhardness tests, SEM and MIP were used to investigate the influences of MK on the phase composition, microhardness of interfacial transition zone(ITZ), microstructural morphology and pore structure of the high-strength concrete (HSC). The results showed that the incorporation of MK promoted the hydration process and decreased the amount of Ca(OH)2 crystals. Furthermore, MK increased the ITZ microhardness of HSC, enhanced the hydrates and improved the bond performance of aggregate and paste. The weak zone between aggregate and paste became almost disappeared when 10% MK was blended. Meanwhile, refinement of the concrete pore structure was obtained in the presence of MK. The improvement of strength and microstructure became more obvious as the MK replacement level increased to 15%.

Abstract: Adding part of granulated blast furnace slag(GBFS), steel salg(SS) , Desulfurization gypsum(DG), we can use Waste Cencrete（WC）as the main raw materials to directly produce uncalcined cement by grinding.With mix proportion 40%~50% of WC and curing in water, the 3d compressive strength of the cement can reach 10MPa.,the 28d compressive strength of the cement can reach 20~40MPa. XRD and SEM analysis show that, the hydration products of the cement are ettringite and C-S-H gel. Parts of WC involves in the hydration reaction, residual WC is wrapped by the hydration product as aggregate filler.

Abstract: Both asphalt concrete (AC) and Portland cement concrete (PCC) are limited in applications in tunnel pavements, due to special conditions in tunnel. To improve the fire resistance, durability and comfort of the tunnel pavements material, rubber particles, lightweight aggregate and polymer were added into PCC. Experimental results showed that physico-mechanical properties such as strength, rigidity, shrinkage and abrasion resistance got worse when rubber particles and lightweight aggregate were added, but when polymer was mixed, the physico-mechanical properties were enhanced dramatically. Microstructure analysis indicated that the interface transition zone (ITZ) influenced the physico-mechanical properties of concrete directly; the ITZ bondage between rubber particles or lightweight aggregate and cement matrix was very poor, which was the main reason for the decline of physico-mechanical properties; when polymer was mixed into the concrete, the ITZ structure were improved, which made the strain energy absorbing function of rubber particles can be exerted entirely, the flexibility and the strength of ITZ were boosted, thereby the physico-mechanical properties of concrete were improved.

Abstract: In this paper the waterproofness of desulfurization building gypsum had been improved by polyacrylamide(PAM) emulsion. The effect of dosage and molecular weight of PAM emulsion on the physical mechanical properties and waterproofness have been investigated and XRD, SEM have been employed to determine the phase compositions of the material. The results showed that softening coefficient of desulfurization building gypsum increased from 0.34 to 0.69, the compressive strength after soaking in water for 24 h increased from 4.9MPa to 6.1 MPa. The effect of PAM emulsion modification prepared by PAM with molecular 3 million weight of on desulfurization building gypsum are better than with molecular weight of 5 million. The effect mechanism of PAM on desulfurization building gypsum was that PAM reacts with the Ca2+ cations produced desulfurization building gypsum hydration to form the ionic compounds acting as a filler and reinforcement in the porosity of desulfurization building gypsum, and also PAM covered the surface of desulfurization building gypsum particles to prevent the crystallization of CaSO4.2H2O.