Effect of epoxy resin on the intrinsic properties of masonry mortars

The paper presents an assessment on the properties of three different types of masonry mortars, namely Portland cement mortar (CM), polymer cement mortar (PCM) and polymer mortar (PM) of various compositions. The effect of binder content (cement and/or epoxy) on CM, PCM or PM has been explored in the study. An assessment was carried out on the basis of mechanical (compressive, tensile and flexural strength), physical (water uptake, chloride ion permeability), morphological (porosity) and thermal (coefficient of thermal expansion) properties of the mortars. A comparative cost analysis of the mortars is also discussed in this article. The results show that the mechanical strength of both PCM and PM improves markedly with the addition of epoxy resin, and the higher rate of incremental strength is found for PM. Consequently, the chloride ion penetration, water uptake, porosity and thermal expansion of the mortars decrease significantly with the resin content, but the rate of drop in chloride ion penetration, water uptake, porosity and thermal expansion is much higher for PM. The test results indicate that the variation of binder content (epoxy/cement) is found to be the key factor determining the mortar properties and cost.     

再生骨料构成对混凝土性能的影响

通过测试混凝土力学性能和耐久性指标,分析再生骨料构成变化对混凝土性能的影响规律.结果表明:再生砂浆块混凝土28 d前抗压强度较高,长期强度则天然骨料混凝土最高.经过100次冻融循环后,再生骨料混凝土质量损失率均低于5%.天然骨料和再生砂浆块混凝土的抗压强度损失率低于25%,而由30%砖块与70%砂浆块组成的混合骨料混凝土及再生砖块混凝土均超过了限值.各类再生骨料混凝土均可满足P10的抗渗等级要求.其中,天然骨料混凝土抗渗能力最强,其次为再生砂浆块混凝土、再生混合骨料混凝土和再生砖块混凝土;各类混凝土抗氯离子渗透能力与抗渗能力排列顺序一致.以上研究表明,再生骨料中的砖块对混凝土力学性能影响较小,但对耐久性能的负面影响较为显著.     

氧化石墨烯改性水泥砂浆抗氯离子渗透性能

采用快速电通量法及长期氯盐浸泡试验,研究了氧化石墨烯(GO)改性水泥砂浆的抗氯离子渗透性能,分析了电通量与表观氯离子扩散系数之间的关系,并通过扫描电镜(SEM)分析了其微观结构。结果表明:掺入适量的GO能够提升水泥砂浆的抗氯离子渗透性能,当掺量为0.06%(质量分数)时最显著,与无GO的对照组相比,水泥砂浆的电通量和氯离子侵蚀深度分别降低了34.5%和27.2%;长期氯盐浸泡60 d、120 d后,0~5 mm处的自由氯离子浓度最高分别降低了28.4%和15.3%;电通量与表观氯离子扩散系数之间存在良好的线性关系;GO有效调节了水化产物形状,减少了内部孔隙,使其微观结构更加密实,从而提升了水泥砂浆抗氯离子渗透性能。     

焙烧水滑石对砂浆中氯离子渗透的影响

通过3.5%NaCl溶液连续浸泡的方式,从砂浆的孔隙结构和氯离子结合能力两个方面,研究了CLDHs的掺加对水泥砂浆抗氯离子渗透的影响,结果表明:与空白砂浆相比,随CLDHs的掺量增加,砂浆强度在一定程度上有所降低,但孔隙结构密实度相应提高;CLDHs的掺加能够显著提高砂浆的抗氯离子侵蚀能力,砂浆氯离子结合能力提高了20%~36%,氯盐浸泡28 d氯离子的渗透深度减小了26%~35%,且CLDHs掺量不宜过大,以占胶凝材料的3%左右为宜.     

Performance of concrete wharves constructed between 1901 and 1928 at the Port of Montréal

An evaluation of concrete properties of five wharves in the Port of Montréal, constructed between 1901 and 1928, was undertaken to investigate the underlying causes of deterioration. The evaluated wharves consisted of either reinforced concrete caissons or massive concrete elements. The wharves were used in the past either as cargo loading docks or for the storage of various materials, some of which were detrimental to concrete.The evaluation program included visual examination of distressed concrete located above water level and the determination of compressive strength, modulus of elasticity, rapid chloride ion permeability (RCP), water soluble chloride ion penetration profiles, as well as a detailed microstructural examination. This article discusses the various results pertaining to the quality of the concrete and Gunite repairs found in old marine structures such as these, where various modes of degradation were present including ice abrasion, cracking and spalling, alkali-silica reaction (ASR), sulfate attack, and frost damage. These various modes of deterioration affected the quality of concrete in all examined wharves as well as that of previous repair work, demonstrating the need for new repairs. However, despite exhibiting signs of severe damage, the concrete wharves had reasonable strength and elastic modulus values enabling rehabilitation to increase service life.     

苯丙乳液改性砂浆的优化配比及其性能研究

针对工程渗漏、混凝土修补问题,研究了苯丙乳液对水泥砂浆的改性效果.结果表明:砂浆中加入苯丙乳液能够提高抗折强度、抗拉强度和粘结强度,分别提高最大为42.8%、61.8%和1.91 MPa;苯丙乳液对砂浆吸水率影响十分显著,乳液掺量越大,吸水率越小;苯丙乳液能够改善砂浆的抗冻性、抗渗性、抗碳化性、耐腐蚀性和收缩率;龄期42 d,改性砂浆的收缩量减少13.6%;改性砂浆的透水压力为2.4 MPa,提高0.9 MPa;改性砂浆的氯离子渗透高度减少13.6%,且乳液掺量越大,氯离子的渗透高度越小.     

改性混凝土试验及性能研究

针对废弃混凝土中的再生骨料表面附着大量残留的水泥浆,以及新老砂浆之间缝隙过大,进而导致再生混凝土的耐久性能出现问题,结合粉煤灰的特点,提出对再生骨料进行改性处理,在混凝土中掺入一定量的粉煤灰,从而填充再生骨料存在的缝隙过大的问题。最后,利用电通等试验方法对改性混凝土试件的抗氯离子渗透性能进行测试,并通过实验结果表明粉煤灰可改善再生混凝土结果,提高抗渗透性能,并当掺量在28%时,抗氯离子渗透性能最佳。     

Chloride penetration of concrete impregnated with various linseed oil/mineral spirits combinations

Concrete test cylinders (3 × 6 in., or 7.6 × 15.2 cm) dried in a forced air oven or with a gas fired infrared heater were impregnated with different boiled linseed oil/mineral spirits mixtures. The impregnated cylinders, along with nonlinseed oil impregnated cylinders, were contaminated with a saturated sodium chloride solution. Chloride content determinations were performed on mortar specimens obtained at various depths from the surface of the cylinders. Chloride contents determined on the controls indicated chloride levels much higher than probably would have occurred in actual field concrete. The data on linseed oil mixture impregnated concrete indicate that chloride ion penetration into the concrete is significantly reduced as compared to the control specimens.     

干湿交替氯盐环境下氧化石墨烯水泥砂浆抗侵蚀研究

抗氯离子侵蚀能力的强弱对水泥基材料服役寿命长短有着关键性的影响。本文研究了不同氧化石墨烯(GO)掺量(0%、0.02%、0.04%、0.06%、0.08%、0.10%,质量分数)在干湿交替氯盐环境下对水泥砂浆抗氯离子侵蚀性能的影响,分析了不同GO掺量下自由氯离子浓度与水泥砂浆抗氯离子侵蚀性能之间的关系,并利用扫描电子显微镜从微观角度分析水泥砂浆的抗侵蚀性能。结果表明:GO能显著提高水泥砂浆的抗氯离子侵蚀能力,最佳掺量范围为0.04%~0.06%;在同一钻孔深度处,水泥砂浆内的自由氯离子浓度随着GO掺量的增加先降低后升高;GO能有效调节水泥砂浆的微观形貌,减少内部孔隙产生,密实结构,提高水泥砂浆抗氯离子侵蚀能力。     

Effectiveness of cement and plaster layers in protection of FRP confined concrete exposed to high temperatures

In recent years, fiber-reinforced polymers (FRPs) materials have shown great potential as materials for repair and reinforced concrete structures such as beams or columns by externally bonding FRP sheet(s) onto the surface of substrate concrete structures. However, the performance of FRP systems exposed to fire is a serious concern due to the combustibility of FRPs. This study introduces the results of an experimental investigation on the behavior of the circular columns of concrete under a load of axial compression, confined by an envelope of composite materials (carbon fiber and glass fiber) and protected by a layer of mortar cement or plaster coating, after they have been subjected at various temperature (23, 120, and 350 °C). The specific objectives of this study are verifying the applicability and the effectiveness of the proposed technique to improve the behavior of concrete in fire resistance and evaluate the effect of composite materials and the layer coating type used. The results indicated that protecting heat circular confined columns, with a layer of mortar cement or plaster has a significant effect on the axial strength and the ductility. It was shown that the ultimate load and axial strain of heated columns can be restored up to the original level or greater than those of unheated columns. However, the effect of a layer of plaster is more significant than a layer of mortar cement. So this coating system would enhance fire resistance of the FRP, safety and reliability of FRP reinforced concrete structures.     

Permeability characteristics of carbonated concrete considering capillary pore structure

During carbonation process, the calcium phases present in cement are attacked by CO₂ and converted into CaCO₃ and the permeability of concrete is changing due to the change in porosity. The rate of carbonation depends upon porosity and moisture content of the concrete. Especially in underground reinforced concrete structures, the interior portion of concrete surface may be exposed to carbonation and the exterior portion of concrete surface exposed to wet soil or underground water. As carbonation proceeds from outer surface into internal portion of concrete, microstructure is also changed continuously from outer surface into internal portion of concrete. Even the deteriorations in the structures due to the carbonation have been reported more, research on permeability characteristics of concrete considering carbonation and micro-structural information is very scarce.In this study, the permeability coefficient in carbonated concrete is derived by applying a capillary pore structure formation model in carbonated cement mortar and assuming that aggregates do not affect carbonation process in early-aged concrete as a function of porosity. The permeability obtained from the micro-level modeling for carbonated concrete is verified with the results of accelerated carbonation test and water penetration test in cement mortar.     

Chloride ingress and strength loss in concrete with different PC-PFA-MK binder compositions exposed to synthetic seawater

The paper reports the influence of the composition of Portland cement (PC)-pulverised fuel ash (PFA)-metakaolin (MK) binders on chloride ingress and strength retardation of PC-PFA-MK concrete exposed to synthetic seawater. PC-PFA-MK concrete covering four different total cement replacement levels (10%, 20%, 30% and 40%) and with various MK:PFA proportions was exposed to synthetic seawater for up to 1.5 years. The chloride concentration-penetration depth profiles and change in compressive strength of the concrete for a range of binder compositions and at various exposure times are compared with those of the control PC concrete. It is established that blending the binders in PC concrete and PC-PFA concrete with MK produces concrete with a reduced strength deterioration factor (SDF) and good resistance to chloride penetration when exposed to seawater. The results presented in this paper form part of an investigation into the performance of concrete incorporating both PFA and MK in the binder to produce high performance concrete.     

纳米碳酸钙对水泥石氯离子结合量的影响

混凝土孔溶液中的自由氯离子转化为结合氯离子可有效降低沿海、盐湖地区钢筋混凝土结构中的钢筋的腐蚀程度。以纳米碳酸钙掺量和氯离子浓度为变量,研究了纳米碳酸钙对水泥石氯离子结合量的影响,采用电位滴定法测定结合氯离子含量,根据氯离子等温吸附理论绘制结合氯离子与自由氯离子的拟合关系曲线来分析水泥石的氯离子结合能力,通过XRD和热重分析研究水泥石的氯离子结合机理。结果表明:纳米碳酸钙的掺入提高了水泥石的氯离子结合量,当其掺量达3%(质量分数)时,水泥石的氯离子总结合量最大;随着氯离子浓度的提高,掺纳米碳酸钙的水泥石氯离子结合量会相应增加;纳米碳酸钙的掺入可以加快水泥水化,促进C-S-H凝胶和Friedel's盐的生成,有利于水泥石的氯离子物理吸附和化学结合。     

Properties of concrete produced from multicomponent blended cements

This paper presents a study on the behavior of concrete produced from multicomponent blended cements. These blends were prepared by blending 20–60% ASTM Type I cement with the combination of Class C fly ash and clean coal ash. Two percent to four percent sodium sulfate anhydrite was added to the blends as a chemical activator. Tests were conducted on the prepared concrete for strength development, freezing and thawing resistance, resistance to chloride ion penetration, sulfate resistance, and alkali silica reaction. Test results show that concrete produced from blended cements had equivalent or higher strength than the control mixture at all test ages. Blended cements were effective in controlling expansions due to sulfate attack or alkali silica reaction. They also reduced the deterioration of concrete due to freezing and thawing action and greatly increased the resistance to chloride ion penetration into the concrete.     

Evaluation of chloride penetration in high performance concrete using neural network algorithm and micro pore structure

Chloride attack is one of the major causes of deterioration of reinforced concrete structures. In order to evaluate the chloride behavior in concrete, a reasonable prediction for the diffusion coefficient of chloride ion, which governs mechanism of chloride diffusion inside concrete, is basically required. However, it is difficult to obtain chloride diffusion coefficients from experiments due to time and cost limitations.In this study, a numerical technique for chloride diffusion in high performance concrete (HPC) using a neural network algorithm is proposed. In order to collect comparative data on diffusion coefficients in concrete with various mineral admixtures such as ground granulated blast-furnace slag (GGBFS), fly ash (FA), and silica fume (SF), a series of electrically driven chloride penetration tests was performed. Seven material components in various mix designs and duration time are selected as neurons in a back-propagation algorithm, and associated learning of the neural network is carried out. An evaluation technique for chloride behavior in HPC using the obtained diffusion coefficients from the neural network algorithm is developed based on, so-called, Multi-Component Hydration Heat Model (MCHHM) and Micro Pore Structure Formation Model (MPSFM). The applicability of the developed technique is verified by comparing the analytical simulation results and the experimental results obtained in this study. Furthermore, this proposed technique using the neural network algorithm and micro modeling is applied to available experimental data for verification of its applicability.     

玄武岩纤维改善再生混凝土抗氯离子渗透性能研究

为研究玄武岩纤维对再生混凝土抗氯离子渗透性能的影响,本文对4种玄武岩纤维体积掺量(0%、0.2%、0.4%、0.6%)下5个粗骨料质量替代率(20%、40%、50%、60%、80%)的再生混凝土及1组普通混凝土进行了电通量试验,并利用傅里叶变换红外光谱(FTIR)和压汞法(MIP)从水泥水化和孔结构的角度探究了玄武岩纤维对再生混凝土抗氯离子渗透性能影响的微观机理。结果表明,玄武岩纤维显著提高了再生混凝土抗氯离子渗透性能,其中玄武岩纤维掺量为0.2%,粗骨料质量替代率为50%时改善效果最好且优于普通混凝土。基于FTIR发现玄武岩纤维是通过改变再生混凝土水化产物C-S-H的聚合度和CaCO₃的生成而改善其抗氯离子渗透性能。通过MIP得出最优组合掺量下,再生混凝土的孔径分布得到优化,孔隙率最小,进而提高了其抗氯离子渗透性能。     

硅烷偶联剂对复合水泥砂浆性能的影响

通过红外光谱分析及砂浆强度测试，研究了硅烷偶联剂对不同种类复合水泥砂浆的稠度、分层度、抗折强度及抗压强度的影响。结果表明，加入硅烷偶联剂能提高普通水泥砂浆、苯丙胶乳改性水泥砂浆的抗折强度和抗压强度；当硅烷偶联剂质量分数为0．5％时，普通水泥砂浆的抗折强度和抗压强度达到极大值，提高约10％；当硅烷偶联剂质量分数为1％时，苯丙胶乳改性水泥砂浆的抗折强度和抗压强度达到极大值，提高约20％；同时，硅烷偶联剂还能增大普通水泥砂浆和苯丙胶乳改性水泥砂浆的稠度，但砂浆的分层度略有增大。加入经硅烷偶联剂处理的钢纤维，能够提高普通水泥砂浆及苯丙胶乳改性水泥砂浆的抗折强度和抗压强度；当钢纤维用硅烷偶联剂质量分数为1％的硅烷偶联剂水溶液处理时，钢纤维增强砂浆的抗折、抗压强度达到极大值，提高10％以上。     

用原位合成吸水性树脂表层处理方法提高混凝土耐硫酸盐腐蚀性

硫酸盐腐蚀是导致混凝土耐久性劣化的一个重要因素.用原位合成吸水性树脂对混凝土表面处理,为改善混凝土耐硫酸腐蚀提出了一种新方法,即利用高吸水性树脂预聚溶液浸渍混凝土,经红外辐射引发自由基共聚反应原位合成吸水性树脂,通过合成的吸水性树脂吸水膨胀、密实微裂缝或孔隙,截断硫酸盐侵蚀性介质的传输路径提高混凝土抗硫酸盐腐蚀能力.通过试验,研究了硫酸钠溶液在水泥砂浆(处理前后)中的渗透状况,并利用扫描电镜、X射线衍射分析了混凝土受硫酸盐腐蚀的特征.结果表明:用原位合成高吸水性树脂处理砂浆后,能显著降低50 g/L硫酸钠溶液在水泥砂浆内部的渗透速度;经50次硫酸钠溶液干/湿循环处理后的水泥砂浆表现出良好的抗硫酸盐腐蚀性能.     

干湿交替对混凝土中氯离子分布影响的多相耦合数值分析

钢筋混凝土结构的耐久性会因为氯盐侵蚀而受到严重影响。为研究环境湿度对混凝土中氯离子分布的影响,建立了多相耦合的氯离子侵蚀模型,利用数值模拟方法探讨了氯离子侵蚀过程随环境湿度变化的规律。结果表明,环境湿度的改变不仅使混凝土中含水率产生变化,而且对混凝土中氯离子的分布产生显著影响,尤其是会引起孔隙中盐分结晶,这是混凝土性能退化的主要原因之一。数值模拟结果可为混凝土结构的减防腐蚀灾害设计提供重要的参考。     

Performance of volcanic ash and pumice based blended cement concrete in mixed sulfate environment

The deterioration of concrete structures due to the presence of mixed sulfate in soils, groundwater and marine environments is a well-known phenomenon. The use of blended cements incorporating supplementary cementing materials and cements with low C₃A content is becoming common in such aggressive environments. This paper presents the results of an investigation on the performance of 12 volcanic ash (VA) and finely ground volcanic pumice (VP) based ASTM Type I and Type V (low C₃A) blended cement concrete mixtures with varying immersion period of up to 48 months in environments characterized by the presence of mixed magnesium-sodium sulfates. The concrete mixtures comprise a combination of two Portland cements (Type I and Type V) and four VA/VP based blended cements with two water-to-binder ratio of 0.35 and 0.45. Background experiments (in addition to strength and fresh properties) including X-ray diffraction (XRD), Differential scanning calorimetry (DSC), mercury intrusion porosimetry (MIP) and rapid chloride permeability (RCP) were conducted on all concrete mixtures to determine phase composition, pozzolanic activity, porosity and chloride ion resistance. Deterioration of concrete due to mixed sulfate attack and corrosion of reinforcing steel were evaluated by assessing concrete weight loss and measuring corrosion potentials and polarization resistance at periodic intervals throughout the immersion period of 48 months. Plain (Type I/V) cement concretes, irrespective of their C₃A content performed better in terms of deterioration and corrosion resistance compared to Type I/V VA/VP based blended cement concrete mixtures in mixed sulfate environment.