Experimental study on the failure mechanism of recycled concrete

In this study, Young's modulus, strength, and peak strain of recycled concrete under both compressive and tensile loading were experimentally studied to understand its failure mechanism. Due to the different colors of natural aggregates, old hardened mortar, new hardened mortar, and interfacial transition zone (ITZ), the quantity and the distribution of each phase were analyzed by images processing and analysis of cut sections. With the tests, the failure processes and crack situation of the recycled concrete under tensile and compressive loadings were illustrated. It was found that some mechanical properties of recycled concrete are similar to those of mortar, for instance, lower Young's modulus, higher peak strain and more brittleness, due to a larger volume content of both new and old hardened mortar. When compared with old hardened mortar, new hardened mortar has more significant influence on both the strength and the Young's modulus of recycled concrete.     

Influence of the kneading water content in the behaviour of single-coat mortars

The effect of water content in the kneading process of mortars for application as single-coat renders was evaluated in terms of several properties. These properties refer to the mortar product in the fresh and hardened state. Characteristics under evaluation in function of kneading water are, for fresh mortar, the apparent density and entrained air while, for hardened products, apparent density, shrinkage, mechanical properties, abrasion wear and permeability amongst others. If some of these characteristics are obtained by standard tests, others, like abrasion wear, had to be adapted and are described here.Both for fresh and hardened products characteristics, kneading water amount significantly changes them and it was possible to establish the proper content of water to be used in order to get a well-behaved single-coat mortar.     

Evaluation of mixing and application process parameters of single-coat mortars

The effects of different preparation and application conditions of single-coat mortars in their characteristics as fresh and hardened products are described in this work. The parameters under consideration were mixing water, mixing and resting time of the fresh mortar. Tests were made in the fresh mortar like apparent density, amount of entrained air and water retention. Tests with the hardened mortar also included mechanical strength and capillarity evaluations. Finally, practical cases were considered and here some application parameters were studied. It was possible to conclude on some important parameters affecting both the processing and application of single-coat mortars.     

减水剂对磷石膏基胶凝材料性能影响研究

磷石膏基胶凝材料在使用时,工作性能较差,需要加入减水剂来改善工作性.而磷石膏胶凝材料对现有的混凝土减水剂的存在适应性不良的问题.为了深入了解减水剂对磷石膏基胶凝材料的匹配性,本文探究了萘系、聚羧酸和脂肪族类三种减水剂及掺量对磷石膏基砂浆材料各项性能的影响规律.通过对砂浆浆体的流动度、硬化体的力学性能,以及28d吸水率和...     

A model law for the notch sensitivity of brittle materials

In this paper a model law for the notch sensitivity of brittle materials, for instance hardened cement paste, mortar or concrete is presented. This model law shows that notch sensitivity is a necessary however not a sufficient condition for the applicability of linear elastic fracture mechanics. The model law indicates that notch sensitivity of a brittle material decreases with increasing fracture toughness, decreasing tensile strength and decreasing specimen size. The model law explains the increase of the net failure stress of notched specimens with increasing notch depth after passing through a minimum. Such behavior frequently has been observed in experiments on hardened cement paste, mortar and concrete specimens. Results of flexure tests on notched and unnotched hardened cement paste specimens and concretes of various sizes are in accord with the model law.     

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。     

无皂乳液VAC/DMC/VHE-水泥基复合材料的性能研究

研究了无皂乳液醋酸乙烯酯(VAC)/甲基丙烯酰氧乙基三甲基氯化铵(DMC)/乙烯基羟丁基醚与水泥共混所形成的水泥基复合材料的性能。研究发现,聚灰比为5%或10%时,该复合材料的抗折强度都有相应的提高,而抗压强度变化不大。与较早研究的2种无皂乳液与水泥共混所形成的复合材料比较,有更好的性能。     

Evaluation of various cellulose ethers performance in ceramic tile adhesive mortars

Eleven cellulose ethers (CE) were selected and tested in a cement based ceramic tile adhesive (CTA) formulation designed to highlight the effect of the CE on the end-use values of the mortars. Results showed that the end-use values, either in the fresh or hardened state, are strongly influenced by the latex powder/CE choice. This is due to the competitive adsorption between these two components; in the fresh state, it affects the CE concentration in the pore solution and hence the viscosity of the mortar, setting time, and skinning. In the hardened state, when CE films do not prevent evaporation at the tile–mortar interface, adhesion in hot curing conditions is lowered compared to dry tensile adhesion values. Test results showed that CTA formulations should be thought of in terms of the CE/latex powder couple, since interactions between this couple and the cement, strongly influence end-use values of the mortar.     

在混凝土中掺用活性工业废渣改善界面效应和性能的研究

本文利用X射线衍射、压汞测孔等方法研究了在水泥浆体和混凝土中掺入硅灰、赤泥、矾泥、液态渣等活性工业废渣对混凝土界面效应区内Ca(OH)_2的取向指数、水泥浆体的孔径分布及水泥混凝土性能的影响。研究表明,由于这些工业废渣的掺入,大大减小了混凝土的界面效应区,提高了水泥浆体和混凝土的强度,对增强混凝土的抗冻性有很大益处。     

生物质灰对水泥硬化浆体抗压强度影响的试验研究

对比研究了生物质灰与普通粉煤灰在粒度分布、颗粒形态、化学组成、活性指数等方面的不同,并开展了不同掺量生物质灰对水泥硬化浆体抗压强度的影响研究.结果表明:生物质灰颗粒形状不规则、平均粒径及粒径分布范围较大,具有特有的细长纤维状颗粒,且其活性组分Al2O3不足普通粉煤灰的三分之一;生物质灰的火山灰活性小于普通粉煤灰;相同掺量下,生物质灰-水泥复合胶砂各龄期的抗压强度均小于普通粉煤灰-水泥复合胶砂,生物质灰掺量越大,复合胶砂的强度相比纯水泥组下降程度越大;与普通粉煤灰相比,掺加生物质灰的硬化水泥浆体微观结构更为疏松多孔,特别是其特有的细长纤维状颗粒的存在.     

处理刚玉集料对砂浆界面结构的改进

从微观形貌和水化产物、界面电导特性参数以及孔结构等三方面,研究了处理刚玉集料砂浆中界面区的结构特征,并与硅酸盐水泥熱料集料砂浆、标准砂集料砂浆等界面区的结构进行了比较。结果表明,处理刚玉集料在砂浆中发生了水化反应,水化产物对界面区产生致密作用,使得界面区成为砂浆中一个比较致密的区域。     

Binding of chloride in mortar containing admixed or penetrated chlorides

The binding of chloride in mortar samples was studied by chloride analysis and differential scanning calorimetry. It was found to depend on whether chlorides had been admixed to the fresh mortar or ingressed into the hardened mortar from the environment. The chemically bound chlorides can be released into the paste pore solution by electrochemical extraction of the dissolved chlorides. The electrochemical chloride extraction technique, which is considered as an alternative to cathodic protection as method for halting corrosion was found to be capable of removing some of the originally bound chlorides in addition to the dissolved ions. The efficiency of this process depends on the type of the original chloride exposure.     

环氧水泥砂浆的改性机理

通过对环氧改性水泥净浆的水化程度和砂浆的孔结构研究，借助于扫描电镜分析，探讨了聚合物对水泥砂浆的改性机理。聚合物的存在一方面延缓了水泥的水化速度，另一方面改善了硬化浆体的毛细孔结构，一部分聚合物在硬化浆体中形成不连续的薄膜。所以聚合物的改性作用是上述两方面的综合作用。     

高吸水性树脂对水泥砂浆体积收缩及力学性能的影响

将自行研制的高吸水性树脂加入砂浆配方,研究了高吸水树脂对不同水灰比下新拌砂浆的流动度、砂浆存下燥养护过程中的体积收缩以及力学性能的影响.研究发现:高吸水性树脂的加入一定稃度上降低了砂浆的流动度:砂浆在干燥养护时,在水灰比(质量比)为0.5~0.7范围内,砂浆的总体积收缩与水灰比关系不大,高效减水剂多聚羧酸酯的加入能增大砂浆的体积收缩;在水灰比为0.5～0.6的砂浆下燥养护时,将高吸水性树脂加入到砂浆中町以明显减小其体积收缩;而对水灰比为0.7的高水灰比砂浆的体积收缩改善作用不明显;对于水灰比为0.7的高水灰比砂浆,高吸水性树脂的加入导致其二次浸水时的吸水率增大.此外高吸水性树脂的加入能提高十燥情况下养护后砂浆的力学性能,尤其在较低水灰比的砂浆中作用更为明显.     

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.     

Experimental study of micro/macro crack development and stress-strain relations of cement-based composite materials at elevated temperatures

This paper presents the results of observations of scanning electron microscope (SEM) micro/macro crack development and simultaneous measurements of temperature-dependent stress-strain relations of hardened cement pastes (HCP) and mortar under a steady thermal state (up to 500 °C) and a displacement-controlled loading process. The experimental results showed that the thermal damage of HCP was not only due to the recognized decomposition of the hydration products but also to the formation of dehydration-induced microcracks. These damage mechanisms, together with three other types of macrocracks arisen from the mismatch of expansion/shrinkage between the phase materials (HCP and aggregates) contributed to the thermal damage of the mortar. By comparing the evolution of the stress-strain curves for the HCP and the companion mortar specimens, the effects of the damage mechanisms could be separately quantified. In this study, the thermal damage of the mortar specimens was largely caused by the thermal mismatch mechanism.     

早龄期磷酸钾镁水泥砂浆的抗冻性评价

为了研究早龄期磷酸钾镁水泥(MKPC)砂浆的抗冻性,测试了在水和5%(质量分数)Na₂SO₄溶液中快速冻融早龄期MKPC砂浆试件的强度、体积变形和吸水率,分析了其物相组成和微观形貌,并将其与水化28 d的MKPC砂浆试件相比较。结果表明,快速冻融循环环境下,早龄期MKPC砂浆试件(水化龄期超过1 d)的强度衰减程度低于水化28 d的MKPC砂浆试件,经受225次冻融循环后,早龄期MKPC浆体试件的剩余强度与28 d水化龄期的MKPC砂浆试件接近,在硫酸盐冻融循环环境下MKPC砂浆试件的强度衰减程度低于水冻融循环环境下的MKPC砂浆试件。早龄期MKPC砂浆试件(水化龄期超过1 d)在冻融循环环境下有较好的抗变形能力,且明显优于水化龄期28 d的MKPC试件。水冻融循环环境下MKPC砂浆试件的抗变形能力优于硫酸盐冻融循环环境下的MKPC砂浆试件。冻融循环过程对水化28 d的MKPC砂浆硬化体孔结构的劣化作用强于水化1 d的MKPC砂浆硬化体。经受硫酸盐冻融循环的MKPC砂浆硬化体的开口孔隙率低于同条件的水冻融循环MKPC硬化体。     

Acoustic Emission in the Drying of Hardened Cement Paste and Mortar

Acoustic emission (AE) during the drying of cement and mortar was studied extensively; AE in direct fracture of notched beams was also measured. A new method for observing the hydration of cement by measuring acoustic conductivity was developed and used to aid in the interpretation of the drying experiments. Acoustic emission due to drying increased rapidly with the time of hydration. It reached a maximum value at ∼60 days for hardened cement paste and 240 days for a standard mortar. It is shown to be caused by fractures in structures that develop, at least in part, during the drying process.     

含浆量对再生混凝土性能及强度的影响

再生集料表面包裹着一层硬化水泥砂浆、导致再生混凝土的强度变化较复杂。利用集料的吸水率指标来探讨如何利用吸水率、取代率来推算含浆量以及不同含浆量的再生集料对混凝土7d、28d强度;再生混凝土的强度与灰水比的线性关系和工作性能的影响。     

磷渣矿化熟料的水化凝结和硬化特征

通过物性检测、ＤＴＡ、ＸＲＤ、ＳＥＭ分析和孔结构测试等，对以磷渣作为矿化剂煅烧的硅酸盐水泥熟料水化、凝结硬化特征进行了研究，认为矿化熟料中Ａ矿数量增多，发育良好，尺寸适当，加上Ｐ２Ｏ５的固溶作用，使其水化活性有所提高，是获得早强、高强的内在原因。