Delayed ettringite formation (DEF) in mortars of white cement

In this study white cement CEM I-52.5 and white limestone cement CEM II-LL, A and B, with 15% and 25% limestone substitution, were studied. The way delayed ettringite forms, due to exposure to high temperatures (50 °C) and external sulphate attacks, was examined in the mortar samples.The mortars were immersed at 50 °C for 180 days in: (a) a saturated Ca(OH)₂ solution and (b) a 5% Na₂SO₄ solution. During the experiment’s duration, the mortar samples were being observed visually on a regular basis while their expansion was estimated on a weekly basis by measuring the change of length with a micrometer. At the end of the experiment, the mortar samples’ compressive strength was determined and the deterioration products were identified through means of X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM-EDAX), Thermogravimetry (TG) and Infra-Red Spectroscopy (FT-IR).Concluding it is evident that the amount of ettringite is proportional to the C₃A content of cement. Sulphates amount in cement is the controlling factor for heat induced ettringite formation since when they are consumed the reaction stops. On the other hand in the case of external sulphate attack another important controlling factor is the compressive strength of the cement; the higher compressive strength the lower the risk of expansion. Finally, in the case of external sulphate attack, limestone, when added to cement, was proved to enhance the durability against sulphates attack when compared to a cement of the same class.     

Long-term evolution of delayed ettringite and gypsum in Portland cement mortars under sulfate erosion

The magnitude evolution of ettringite and gypsum in hydrated Portland cement mortars due to sulfate attack was detected by X-ray powder diffraction. The influences of sulfate concentration and water-to-cement ratio on the evolution of ettringite and gypsum were investigated. Experimental results show that the magnitude of ettringite formation in sodium sulfate solution follows a three-stage process, namely, the ‘penetration period’, ‘enhance period of strength’, and ‘macro-crack period’. The cracking of concrete materials is mainly attributed to the effect of ettringite. The gypsum formations occurred in two stages, the ‘latent period’ and the ‘accelerated period’. The gypsum formation including ettringite formation was relative to the linear expansion of mortars to some extend. Both water-to-cement ratio and sulfate concentration play important roles in the evolution of ettringite and gypsum.     

Performance of limestone cement mortars in a high sulfates environment

With the aim of studying the influence of cement composition on resistance in high sulfates environment, standard mortars have been produced using ordinary Portland cement (CEM I – 32.5) and limestone cement with 35% limestone (CEM II/B-LL – 32.5). The pore size distribution of the cement pastes was measured. The mortars were immersed in a 5% Na₂SO₄ solution at 20 °C for 1.5 years and the caused deterioration was been visually observed at a regular basis. Furthermore, the mortars expansion was being estimated by measuring the change of length. At the end of the experiment the compressive strength of the mortars was measured. The deterioration products of the mortars have been identified by means of X-ray diffraction, optical microscopy and environmental scanning electron microscopy. The limestone cement based mortar presented cracking that started at the age of 6 months and continued throughout the experiment. It also displayed high expansion after 250 days of immersion in a 5% Na₂SO₄ caused, as proved using the analytical techniques, by the formation of gypsum and ettringite. Concluding, the cement with 35% limestone did not perform as well as ordinary Portland cement under the most aggressive laboratory conditions. Hence, it is obvious that the addition of limestone in the cement leads to a totally different behaviour than Portland cement with respect to the resistance in high sulfates environment.     

新型环氧树脂乳液改性水泥砂浆性能的研究

研究了环氧树脂乳液对水泥砂浆力学性能的影响，耐酸碱性的影响。采用电子扫描显微镜（SEM）分析了环氧胶乳网络结构与水泥砂浆的作用机理，以及环氧树脂乳液水泥砂浆微观结构形态。     

铁路高地热隧道衬砌混凝土延迟钙矾石生成风险分析

在分析DEF的产生和破坏作用机制的基础上,根据铁路高地热隧道施工过程中温度的变化条件,分别对隧道初支和二衬混凝土或砂浆试件进行DEF加速模拟试验。试验结果表明,采用符合现行铁路混凝土技术标准要求的原材料,并对配制参数进行合理控制的前提下,混凝土或砂浆试件的膨胀率均低于0.04%的安全限值。说明铁路高地热隧道衬砌混凝土产生DEF破坏的风险很低,高地热环境对混凝土耐久性的影响较小。     

Effect of under water storage on bridge formation by water-soluble polymers in cement mortars

Polymer film formation in cement mortars modified with small amounts of water-soluble polymers (1% of the cement mass) is studied. A major contribution of the polymer films to the mechanical strength is found. Polymer bridges are detected between the layered Ca(OH)₂ crystals, on top of the cement hydrates at the air void surfaces and intermingled with the cement hydrates. Because water-soluble polymer films are highly sensitive to moisture and water, the effect of under water storage on the bridge formation is important towards the practical applications. A serious decrease of the flexural and splitting tensile strength is observed during intensive storage at high relative humidity or under water. The polymer bridges are leached under water and deposed in free spaces of the cement matrix upon subsequent drying.     

提高试验室温、湿度控制水平适应水泥胶砂强度检验方法(ISO)要求

自2001年4月1日起强制实施的GB/T 17671-1999<水泥胶砂强度检验方法(ISO法)>,对试验室温、湿度控制条件提出了更严格要求.为什么要规定这种严格要求,怎么样达到这种严格要求,是广大水泥试验室关心的问题,现就此简述如下.     

Bioaccumulation profiles of S-labelled sodium alkylpoly(oxyethylene) sulfates in carp (Cyprinus carpio)

The uptake, distribution and elimination of two labelled surfactants, ³⁵S-labelled sodium dodecyltri(oxyethylene) sulfate (³⁵S-C12-AES(3)) and ³⁵S-labelled sodium dodecylpenta(oxyethylene) sulfate (³⁵S-C12-AES(5)) were investigated in carp (Cyprinus carpio) exposed to concentrations of 0.3–0.6 mg l⁻¹, using whole-body autoradiography and the liquid scintillation counting method. ³⁵S-Radioactivity was first rapidly absorbed by the gills and skin and transferred to other organs and tissues. After 24 h-exposure, there was a comparatively high accumulation of ³⁵S-radioactivity in the gills, hepatopancreas, gall bladder, intestinal content, and nasal and oral cavity. The distribution patterns of ³⁵S-radioactivity derived from ³⁵S-C12-AES(3) and ³⁵S-C12-AES(5) in tissues and organs were similar. The whole-body concentration factors of ³⁵S-radioactivity in fish exposed to ³⁵S-C12-AES(3) and ³⁵S-C12-AES(5) for 72 hr were 18 and 4.7, respectively. In surfactant-free water, the absorbed ³⁵S-radioactivity was eliminated more rapidly from the fish body exposed to ³⁵S-C12-AES(3) than ³⁵S-C12-AES(5). It was eliminated relatively fast from gills and hepatopancreas, but elimination from gall bladder was rather slow.     

水泥基复合材料中SO3与Al2O3含量对钙矾石及膨胀性能影响的研究

本文通过水泥基复合材料水泥,膨胀剂,粉煤灰,引气剂,高效减水剂中SO3与Al2O3含量对钙矾石及混凝土膨胀性能的影响进行了研究,指出了SO3与Al2O3及其比值对膨胀性能影响的重要性,试图使人们在使用补偿收缩混凝土前事先确定膨胀量,再根据膨胀量去确定水泥基复合材料中的SO3与Al2O3含量,从而达到由定性到定量的转变。     

浅谈白水泥厂立磨常见故障及处理对策

立磨在水泥生产中,被广泛用于生料的粉磨工艺,主要优点是产量高、磨耗小,由于带进产品的铁含量低,因而特别适合粉磨白水泥的生料。我厂(前身广州市建材一厂)在1995年安装使用MLY—14立磨用于白水泥生产,经过几年的实践,总结了一些使用经验,使初期较多出现的问题逐步得到解决,效果较为满意。现就立磨在白水泥生产中常见的几个问题及对它的改革谈几点体会:1 解决立磨生产过程中常见的几个问题1.1漏风问题立磨的粉磨原理是由辊子对物料进行压碎和辗磨。当物料经给料器送入磨腔落到磨盘上,旋转着的磨盘把物料带到辊子底下,在辊子自身的重力和…     

Small-Scale Test Protocol for Firefighting Foams DEF(AUST)5706: Effect of Bubble Size Distribution and Expansion Ratio

The experimental program described in this paper sought to assess the suitability of the small scale DEF(AUST)5706 standard for measuring the suppression and burnback performance of Class B foams on pool fires. DEF(AUST)5706 is an Australian Defence standard mandatory for use by the Australian Navy, Army and Air Force. The test protocol required the measurement of the 3/4 control, extinguishment and 1/3 burnback times for a circular pan of aviation gasoline (AVGAS 100/130), 0.28 m² in surface area. The test program involved compressed-air foams (CAF) and aspirated foams of two expansion ratios, and employed two AFFF formulations: a 6% telomer concentrate and, to obtain base-line measurements, 3% PFOS FC-600 concentrate which was manufactured by the 3 M company prior to the PFOS phase out. At lower expansion (7:1), the aspirated and compressed-air foams demonstrated similar fire control performance, whilst more expanded (9:1) CAF was generally more efficient at extinguishing, but less efficient in controlling the fire. CAF formed a better seal over the fuel surface and at the hot pan walls, and these foams performed noticeably better than aspirated foam against fuel re-ignition. The paper links these observations with the underlying distributions of bubble sizes, which were measured and fitted to modified Rosin/Rammler cumulative volume distribution functions. We propose that a modified version of DEF(AUST)5706 be adopted as a universal small-scale test protocol.     

Effect of temperature on porosity and on chloride diffusion in cement pastes

This paper is related to the effect of temperature upon the diffusive properties and the microstructural features of cementitious materials. Our experimental studies aim at linking the transport properties to the porosity and the cracks network of the microstructure.

The studied materials were three cement pastes having different water to cement (W/C) ratios (W/C = 0.35, 0.45 and 0.60). Rise of temperature in concrete structures was simulated by heating at different temperatures (45 °C, 80 °C and 105 °C). Evolution of microstructure was essentially characterized by mercury intrusion porosimetry (MIP). Diffusion tests in non-steady-state regime were carried out in order to characterize the diffusive properties. Apparent diffusion coefficients were determined from colorimetric method to follow the ingress of chloride and an analytical solution of Fick’s second law.

Our results showed that rise of temperature induced macroscopic cracking network and modification of pore size distribution. As a consequence, the transport properties were modified by thermal treatment. These modifications were mostly explained by the increase of capillary porosity.     

Bioaccumulation profiles of 35S-labelled sodium alkylpoly(oxyethylene) sulfates in carp (Cyprinus carpio)

The uptake, distribution and elimination of two labelled surfactants, ³⁵S-labelled sodium dodecyltri(oxyethylene) sulfate (³⁵S-C12-AES(3)) and ³⁵S-labelled sodium dodecylpenta(oxyethylene) sulfate (³⁵S-C12-AES(5)) were investigated in carp (Cyprinus carpio) exposed to concentrations of 0.3–0.6 mg l^?1, using whole-body autoradiography and the liquid scintillation counting method. ³⁵S-Radioactivity was first rapidly absorbed by the gills and skin and transferred to other organs and tissues. After 24 h-exposure, there was a comparatively high accumulation of ³⁵S-radioactivity in the gills, hepatopancreas, gall bladder, intestinal content, and nasal and oral cavity. The distribution patterns of ³⁵S-radioactivity derived from ³⁵S-C12-AES(3) and ³⁵S-C12-AES(5) in tissues and organs were similar. The whole-body concentration factors of ³⁵S-radioactivity in fish exposed to ³⁵S-C12-AES(3) and ³⁵S-C12-AES(5) for 72 hr were 18 and 4.7, respectively. In surfactant-free water, the absorbed ³⁵S-radioactivity was eliminated more rapidly from the fish body exposed to ³⁵S-C12-AES(3) than ³⁵S-C12-AES(5). It was eliminated relatively fast from gills and hepatopancreas, but elimination from gall bladder was rather slow.     

水泥企业如何实施顾客满意的监视与测量

追求顾客满意,争取超越顾客期望是以顾客为中心原则的明确要求,也是企业实施持续改进的不竭动力.ISO/FDIS 9001:2000版标准8.2.1中明确规定组织应监视顾客对组织是否满足其要求的感知的有关信息,获取和利用这些信息的方法应予以确定.     

路用聚合物改性水泥混凝土(PMC)性能与应用研究

聚合物改性水泥混凝土即具有水泥混凝土的高强度又具有沥青混凝土的高柔性.由于其优良的路用性能,聚合物改性水泥混凝土在路面工程领域得到了广泛的研究与应用.分析探讨了聚合物对水泥混凝土的改性作用以及改性机理,并总结了应用在混凝土中各种聚合物的要求,总结了近年来聚合物在水泥混凝土略面工程中的应用研究现状,最后结合实例具体介绍了聚合物改性混凝土的在路面工程中的施工方法.     

水稳类基层温缩开裂的原因及预防措施

对水泥稳定类基层材料温度收缩的机理、影响因素进行了详细而全面地分析,并在此基础上提出有效的预防措施,以尽量减少水泥稳定类基层材料的温缩裂缝,从而延长建筑物的使用寿命。     

木质纤维在新拌水泥基瓷砖胶粘剂中的应用研究

木质纤维作为一种多功能外加剂在干混砂浆中得到了广泛的应用.参照瓷砖胶粘剂的相关测试方法,研究掺木质纤维对新拌瓷砖胶粘剂的流动度、抗滑移性能、开放时间的影响;测试了不同木质纤维在具有基础黏度水溶液中的黏度,类比其在瓷砖胶粘剂中的流变特性.并分析阐明了木质纤维对新拌瓷砖胶粘剂性能影响的机理.     

Viability analysis and constructive applications of lightened mortar (rubber cement mortar)

The aim of this research project presented here was the suitability assessment using rubber granulation in lightened cement mortars. This rubber granulation was made from worn tyres. It was obtained by mechanical grinding. The uses proposed for this type of mortars in the construction field are as packing material. Therefore, the only condition needed is the low density and easy handling on the construction. From the results obtained, more expensive lightweight aggregates could be substituted by rubber granulation derived from the rejected tyres.     

水泥缓凝剂甘氨酸二(亚甲基膦酸)的合成与应用研究

以甘氨酸(Gly)、亚磷酸和甲醛为原料,通过Mannich反应合成水泥缓凝剂甘氨酸二(亚甲基膦酸).重点考察了单体摩尔比对缓凝剂性能的影响.结果表明,当n (Gly):n(H3PO3):n(HCHO)=1.00:2.05:2.10,甲醛滴加时间为1h,105℃下反应2h时,合成缓凝剂的缓凝效果最佳.并从水泥水化的角度研究了缓凝剂的缓凝效果,能够有效降低水泥的水化放热速率和放热量,延缓水化放热峰值的出现.与减水剂的复配研究表明,其适应性好,且有一定的辅助保坍功能.     

Effect of silica fume on cement hydration and temperature rise of concrete in tropical environment

Investigated herein is the effect of temperature on heat development in cement pastes and concretes with and without silica fume cured at relatively high temperatures often encountered in tropical environment. With an initial temperature of 30°C, adiabatic temperature rise of the concrete with 8% silica fume as cement replacement was similar to that of the control Portland cement concrete up to about 18 h. After 24 h, however, the temperature of the silica fume concrete was lower than that of the control concrete. Since the concrete with 8% silica fume had a higher 28-day compressive strength (72.5 MPa) than the control concrete without silica fume (59.2 MPa), the concrete with silica fume is likely to have a lower temperature rise as compared with the control concrete of equivalent 28-day strength by reducing cementitious materials content with the same water content. The extent of heat evolution in the silica fume pastes was generally greater at lower temperatures of 20–50°C, but less at 65°C than in the control paste. At the relatively high curing temperatures, the degree of cement hydration in the paste with silica fume was lower than that in the control cement paste at early ages. However, the pozzolanic reaction started even before 24 h after water was added.