The effect of silane-based hydrophobic admixture on corrosion of reinforcing steel in concrete

The influence of a hydrophobic admixture based on silane on the corrosion resistance of steel reinforcement in concrete was studied. Sound or deliberately pre-cracked concrete specimens were manufactured with w/c of 0.45 and 0.80, both in the presence and in the absence of silane. The specimens were fully immersed in a 3.5% NaCl aqueous solution.The results, in terms of electrochemical measurements, visual observations, and weight loss measurements of steel reinforcement, show that silane blocked corrosion process in uncracked concrete specimens. On the other hand, in cracked concrete specimens, corrosion of steel reinforcements was unexpectedly more severe in hydrophobic specimens rather than in the corresponding not hydrophobic ones. It is believed that oxygen, which is needed to feed the corrosion process, diffuses faster in a gaseous phase through the open concrete porosity in the hydrophobic concrete, whereas in concrete without silane, oxygen diffuses much more slowly through the water filling the pores of the saturated concrete.     

Synthesis,characterization, and application of the sodium poly(styrenesulfonate) produced from waste polystyrene cups as an admixture in concrete

Wasted polystyrene (PS) plastic cups were used in the synthesis of sodium poly(styrenesulfonate) (NaPSS). The produced polyelectrolyte was water‐soluble. The viscosimetric molecular weight was 126,146 g mol^?1. The sulfonation of the polymer was estimated through FTIR spectroscopy and chemical analysis of the number of sulfonic groups. The presence of bands at 1326 and 1188 cm^?1 in the infrared spectra was characteristic for sulfonic groups. The polymer was obtained with 60.3% of sulfonation. An aqueous solution of NaPSS was used as an admixture in concrete of portland cement. The results showed that the slump increasing of the concrete was up to 300% with 0.3% content of NaPSS per weight of cement. It was possible to reduce the water content of the concrete in 13.2% using NaPSS solution as an admixture. The compressive strength gain was 23.9% after 28 days of curing. The results indicated that NaPSS, produced from waste PS cups, can be satisfactorily used either as a plasticizer or as an admixture for water reduction in concrete. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1534–1538, 2005     

硅灰对超轻水泥基复合保温材料性能的影响

超轻水泥基复合保温材料(UCIM)是以水泥为胶凝材料,膨胀聚苯乙烯泡沫塑料(EPS)颗粒、掺合料、泡沫剂、改性剂和水等为主要原料,采用物理发泡工艺制备而成。UCIM由EPS颗粒与泡沫混凝土基体互穿构成,不同品种的掺合料等效替代水泥后,能不同程度影响水泥浆体对EPS颗粒的包裹性,从而影响UCIM结构的均匀性与制品性能。通过设计不同掺量的掺合料,对比硅灰、偏高岭土及矿粉所制备的UCIM的均匀性及强度,结果表明,当采用硅灰时,UCIM未产生分层离析现象且制品强度试验结果较好;通过微孔拍摄及强度、热工性能测试,系统研究了硅灰掺量对UCIM的泡沫混凝土基体的孔结构、强度和导热系数的影响,结果表明,适宜掺量的硅灰能提高UCIM的力学性能,使UCIM的泡沫混凝土基体的平均孔径减小,进而有利于降低UCIM导热系数。     

Modeling the hydration of concrete incorporating fly ash or slag

Granulated slag from metal industries and fly ash from the combustion of coal are industrial by-products that have been widely used as mineral admixtures in normal and high strength concrete. Due to the reaction between calcium hydroxide and fly ash or slag, the hydration of concrete containing fly ash or slag is much more complex compared with that of Portland cement. In this paper, the production of calcium hydroxide in cement hydration and its consumption in the reaction of mineral admixtures is considered in order to develop a numerical model that simulates the hydration of concrete containing fly ash or slag. The heat evolution rates of fly ash- or slag-blended concrete is determined by the contribution of both cement hydration and the reaction of the mineral admixtures. The proposed model is verified through experimental data on concrete with different water-to-cement ratios and mineral admixture substitution ratios.     

A volumetric technique for measuring the coefficient of thermal expansion of hardening cement paste and mortar

Knowledge of the coefficient of thermal expansion (CTE) is of paramount importance for the determination of the cracking risk of concrete structures at early ages. This paper presents a novel technique which is suitable to measure the CTE of hardening materials with high accuracy starting from casting time.The technique consists of casting a small amount of cement paste or mortar into flexible membranes. The specimens are immersed in an oil bath, whose temperature is rapidly changed and then kept constant in repeating cycles. By suspending the sample from a high-precision balance and reading the change of mass after each temperature step, the CTE is calculated with high accuracy from the measured temperature and strain.Results on cement pastes and mortars (water/cement 0.3) showed a good repeatability. In particular, a sudden decrease in the CTE at setting time, followed by a gradual increase as the cement paste self-desiccates, was measured.     

内掺硅烷乳液憎水剂对混凝土性能的影响

通过强度测试、水化热实验、热重分析、毛细吸水实验以及压汞实验研究了内掺硅烷乳液憎水剂对混凝土强度以及毛细吸水性能的影响规律及其机理.结果表明:高掺量硅烷乳液一定程度上抑制水泥水化,从而导致混凝土早龄期抗压强度和劈裂抗拉强度下降以及28 d养护后水泥净浆试块中毛细孔的体积增大.毛细吸水实验表明:28 d龄期混凝土毛细吸水...     

氧扩散法研究砂浆或砼的渗透性和开放孔隙率

介绍了能快速简捷地测定砂浆或砼的渗透性的氧扩散法,它可以有效地应用于评估硬化水泥石的开放孔隙率及研究砼的耐久性。研究表明,砂浆试件的氧扩散法测定结果以正常在反映出水灰比、胶凝材料组成、养护条件等因素对水泥石孔结构和渗透性的影响。     

外加剂和粉煤灰对碱式硫酸镁水泥混凝土性能影响研究

利用碱式硫酸镁水泥制备了不同外加剂和粉煤灰掺量的碱式硫酸镁水泥(BMSC)混凝土.研究了外加剂和粉煤灰对BMSC混凝土抗压强度以及抗硫酸盐腐蚀性能的影响,并对BMSC混凝土物相组成和微观形貌进行了分析.结果表明:掺加外加剂后混凝土的强度有大幅度地提高.当外加剂掺量为水泥质量的0.5%时,混凝土的强度达到最大值;继续增加外加剂掺量,对混凝土的强度影响不大.掺加粉煤灰后,混凝土的强度有所下降.且水灰比一定时,粉煤灰掺量越多,对混凝土的强度越不利.掺加外加剂和粉煤灰后,混凝土的抗硫酸盐腐蚀性能得到了明显的改善;且同等条件下,碱式硫酸镁水泥混凝土抗硫酸盐腐蚀性能优于普通硅酸盐水泥混凝土.     

A pulsed field gradient and NMR imaging investigations of the water retention mechanism by cellulose ethers in mortars

The study presented in this paper is devoted to improve the knowledge on the influence of cellulose ethers (CE) on the freshly-mixed mortars water retention. Indeed, this crucial property is the most important imparted by these polysaccharides. One of the assumptions proposed to explain this phenomenon is that CE acts as diffusion barrier to the water. To test this hypothesis, the CE effect on the self-diffusion coefficient of water in solution and on the water mobility between two fresh cement pastes was studied by Nuclear Magnetic Resonance. CE does not significantly modify the water self-diffusion coefficient in CE solution or in admixed cement pastes. Moreover the interdiffusion imaging experiments demonstrated that the water diffusion at the paste/paste interface is not affected by the presence of cellulosic admixture.     

Combined effects of mineral admixtures and curing conditions on the sorptivity coefficient of concrete

The effect of mineral admixture and curing condition on the sorptivity of concrete are investigated. In the present work, the maximum particle size and the grading of coarse aggregate, the cement content and water/cement ratio of the concrete are kept constant. Then, in the ordinary Portland cement (OPC) 42.5 concrete, a portion of the sand is replaced by a mineral admixture such as fly ash (FA), limestone filler, sandstone filler or silica fume (SF). This paper presents the results of both the sorptivity coefficient and the compressive strength of OPC 42.5 concretes with these mineral admixtures, and concretes with OPC 32.5, blended cement (BC) or trass cement (TC). The results obtained indicate that the sorptivity coefficient of concrete decreases as the compressive strength of concrete increases. It is also shown that the sorptivity coefficient of concrete is very sensitive to the curing condition. The effect of curing condition on the sorptivity coefficient of concrete seems to be higher in low-strength concretes.     

Hydrophobic concrete using waste paper sludge ash

The feasibility of using a low-cost super hydrophobic powder as water-resisting admixture or water-repellent surface coating for concrete has been investigated. The powder was produced from paper sludge ash (PSA), a by-product from the manufacture of recycled paper. The effect of hydrophobic PSA on workability, strength and transport properties, including sorptivity, water absorption, diffusivity, permeability and electrical conductivity is reported. Samples were prepared at water/cement ratio of 0.38, cured up to 28 days and conditioned at 50 °C to constant mass prior to testing. It was found that replacing Portland cement with 12% hydrophobic PSA reduced water absorption, sorptivity and conductivity by 84%, 86% and 85% respectively, with no major detrimental effects on hydration, strength and density. When used as a surface coating, the hydrophobic PSA reduced both absorption and sorptivity by 85–99% depending on the adhesive used. Samples surface coated with hydrophobic PSA showed excellent water repelling and self-cleaning characteristics.     

不同掺和方式下的透水混凝土性能探讨

针对传统水泥路面不透水给城市生态环境造成的影响问题,提出一种新型透水混凝土材料,并通过实验了解这种新型混凝土的性能。以陶粒、石子作为粗骨料,采用单掺和复掺的形式,构建不同配合比下的透水混凝土实验组。最后通过性能测试,得到不同水胶比、骨料粒径、目标孔隙率对透水混凝土抗压强度和透水系数的影响,从而为透水混凝土在不同地方的应用提供实验参考数据。     

高性能聚羧酸减缩材料的研发(Ⅲ)——高分子聚合物(HP-SRA)的作用机理

通过对比,研究了采用自行研发的高分子聚合物(HP-SRA)与Eclipse-Floor减缩剂(Eclipse-SRA)2种减缩材料在降低水泥颗粒表面上的平均吸附率、溶液表面张力和蒸发速率、提高溶液动力黏度、减少水泥砂浆收缩和改善孔结构分布等方面的作用。结果表明,水泥颗粒表面对高分子聚合物(HP-SRA)的平均吸附率小于10%;高分子聚合物(HP-SRA)可显著降低溶液表面张力和蒸发速率,大幅提高溶液动力黏度;高分子聚合物(HPSRA)对水泥砂浆减缩效果显著,在其掺入量为0.30%(质量分数)时,水泥砂浆在3 d和28 d养护龄期时的收缩率分别下降了48.6%和20.2%。     

混凝土矿物掺合料的强度效应研究

矿物掺合料对混凝土具有重要的强度效应。本文认为掺有矿物掺合料的混凝土复合材料的强度由水泥混凝土基体（水泥浆体和砂石集料）产生的强度和帮物掺合料的物理和化学两方面效应对强度的贡献两部分构成，据此提出了全面估算混凝土矿物掺合料强度效应的新方法。并从理论和试验两方面分析了水胶化、掺合料掺量以有龄期对矿物掺合料强度效应的影响规律。     

砂基透水混凝土路面砖胶结料试验研究

研究自主研制的胶结料不同掺量、水灰比、集料级配及灰集比对砂基透水混凝土路面砖强度、透水性的影响,并通过室内试验测试试件保水性、抗冻性、耐磨耗性、抗硫酸盐-干湿循环侵蚀.先将自主研制的胶结料Ⅰ与3种同类型胶结料通过胶砂试验比选.结果表明:胶结料Ⅰ(28 d)抗压强度59.2 MPa、抗折强度9.3 MPa,优于同类型胶结料;胶结料Ⅰ掺砂基透水混凝土路面砖最优掺量为水泥质量的5%,其强度为35.6 MPa,透水系数为3.5×10 -2 cm/s,并具有良好的保水性、抗冻性、耐磨耗性和抗硫酸盐-干湿循环侵蚀性能.     

粉磨工艺对水泥颗粒分布及其混凝土性能的影响

研究了不同粉磨工艺系统磨制水泥的颗粒分布、粉磨电耗、标准稠度用水量、与减水剂相容性及其配制的混凝土强度、耐磨性、抗碳化性能的差异;针对我国混凝土行业的现状,从混凝土性能的角度出发,探讨了现阶段各种水泥粉磨工艺的特点。研究结果表明,水泥粉磨工艺系统的效率越高,水泥的颗粒分布越集中,水泥的标准稠度用水量增大,与减水剂相容性变差,在缺乏良好的掺合料进行颗粒分布校正的前提下,所配制混凝土的强度、耐磨性及抗碳化性能均有所下降。     

废弃混凝土中基质胶凝组分作水泥混合材料的研究

采用热处理和加入表面活性剂的方法将废弃混凝土中的骨料与基质胶凝组分进行分离。将分离出的基质胶凝组分（FWC）按照不同配合比掺入水泥熟料中粉磨不同时间测试其性能。结果表明：FWC的易磨性优于水泥熟料，FWC具有较强的水化能力和较好的胶凝性，可以作为一种水泥混合材料。     

Physico-chemical changes in polymer impregnated mortars on exposure to sea water

This paper highlights the results and interpretations of experiments conducted to analyze the effect of sea water on conventional precast cement mortar (OPC) and polymer impregnated mortars (PIC). The precast cement mortars were impregnated with a mixture of methyl methacrylate and 2, 2′-Azobisisobutyronitrile (AIBN) initiator and polymerized using two different procedures: by microwaves and by conventional hot water method. The OPC and PIC specimens were immersed in sea water separately for 7, 14, 21 and 28 days and their strength parameters were calculated. The changes in the microstructure indicated movement of ions into the cement matrix and the presence of fan-like crystals on the surface of cement mortar. The protective polymer coating in the PIC prevented contact of sea water with cement concrete, thereby increasing the durability of the composite.     

复掺混合材对水泥及混凝土性能影响的试验研究

研究了石灰石、矿渣、烧页岩及粉煤灰四种混合材复配对水泥及混凝土性能的影响。试验结果表明,矿渣和石灰石有益于改善水泥的标准稠度用水量、外加剂相容性、混凝土的工作性能及强度,而烧页岩和粉煤灰有益于水泥的强度,几种混合材的合理搭配可以改善水泥和混凝土的性能。     

硫铝酸盐水泥作纤维增强砼的实验研究

预应力纤维增强水泥砼比起不加预应力的有着许优点。但是,由于基质的收缩,应力作用将减少。如果采用硫铝酸盐水泥,可以减少基质的收缩。文章介绍了二组关于硫铝酸盐水泥砼基本物理机械性能的实验,讨论了外加剂对砼性能的影响,并提出:外加剂的比例是制造纤维增强水泥板技术的重要参数。