Compressive strength, chloride diffusivity and pore structure of high performance metakaolin and silica fume concrete

This study is to relate the mechanical and durability properties of high performance metakaolin (MK) and silica fume concretes to their microstructure characteristics. The compressive strength and chloride penetrability of the control and the concretes incorporated with MK or silica fume (SF) at water-to-binder (w/b) ratios of 0.3 and 0.5 are determined. The pore size distribution and porosity of the concretes are also measured. The effect of MK and SF on the interfacial porosity is discussed based on test results. It is found that MK concrete has superior strength development and similar chloride resistance to SF concrete, and the MK concrete at a w/b of 0.3 has a lower porosity and smaller pore sizes than the control (plain) concrete. The resistance of the concretes to chloride ion penetration correlates better with the measured concrete porosity than with the paste porosity. The differences between the measured and calculated concrete porosity is smaller for MK and SF incorporated concrete than for the control concrete, indicating an improvement in the interfacial microstructure with the incorporation of the pozzolanas. This difference is found to be related to the strength and chloride penetrability of concrete to some degree.     

硅质轻型墙板材料受压性能试验研究

GLC硅质轻型墙板是一种新型的复合墙板,为研究其发泡水泥芯材和砂浆的受压性能,进行了4组24块标准试件单轴受压试验,得到了芯材和砂浆试件的破坏形态、全曲线特征、峰值应力、峰值应变、弹性模量,给出材料的应力-应变曲线方程.结果表明:砂浆与芯材的破坏形态主要是劈裂破坏,两者单轴受压应力-应变全曲线下降段有所不同,通过理论分...     

掺矿渣粉和减水剂的HEMC水泥砂浆力学性能

研究了掺矿渣粉和高效减水剂的羟乙基甲基纤维素改性水泥砂浆的力学性能（包括抗压强度、抗折强度、弹性模量、粘结抗拉强度）及其与新拌砂浆体积密度和硬化砂浆孔隙率的关系。掺加减水剂、矿渣粉和羟乙基甲基纤维素后,砂浆的抗压强度与新拌砂浆体积密度和硬化砂浆孔隙率密切相关,抗折强度与之部分相关,粘结抗拉强度则与之无关。减水剂和矿渣粉可增加砂浆的密实度,减小孔隙率,从而使砂浆的抗压强度、抗折强度、粘结抗拉强度和弹性模量得到提高;羟乙基甲基纤维素虽可保持砂浆的粘结抗拉强度稳定,但却使抗压强度和弹性模量降低,减小剂、矿渣 粉和羟乙基甲基纤维素的共同作用,即增加了砂浆的粘结抗拉强度,又使砂浆有足够的抗压强度、抗折强度和弹性模量,当羟乙基甲基纤维素掺量被抑制在一定范围内时,砂浆便可用作混凝土桥面材料及其修补材料。     

建筑垃圾细料生产流动化回填材料的性能

以灰砂比0.03、0.05和0.08,粉砂比0、0.05、0.1、0.15和0.2为设计参数,对建筑垃圾回填材料进行设计。通过试验对回填材料的流动性(流动度、泌水率)、无侧限抗压强度以及应力应变曲线、本构关系模型和弹性模量等进行研究。研究结果表明:回填材料的流动度受水固比影响较大,两者接近线性关系;流动度在200~250mm范围,泌水率在4%~8%之间;回填材料抗压强度与灰砂比和水固比之间存在很好的幂指数关系;回填材料应力应变曲线形状与普通混凝土的相似,在此基础上提出回填材料的本构关系模型;回填材料无侧限抗压强度与弹性模量之间存在很好的指数关系。     

海水侵蚀后水泥砂浆的单轴动态力学性能研究

对经海水侵蚀后的水泥砂浆试件进行单轴动态压缩试验,研究应变速率、侵蚀溶液的类型和浓度对水泥砂浆的应力–应变曲线、极限抗压强度、峰值应变和弹性模量的影响。研究结果表明,水泥砂浆的强度随着应变率的增加而提高,水泥砂浆的强度越低,其强度对应变率更加敏感;随着应变率的增加,水泥砂浆的峰值应变会逐渐增加,但弹性模量会出现先增加后减小的变化规律。应变加载速率对经海水侵蚀后水泥砂浆的应力–应变曲线和强度的影响,与水灰比、侵蚀介质的类型、浓度和侵蚀时间有很大关系。     

Effect of Granulated Blast Furnace Slag and fly ash addition on the strength properties of lightweight mortars containing waste PET aggregates

In this work, the effect of Granulated Blast Furnace Slag (GBFS) and fly ash (FA) addition on the strength properties of lightweight mortars containing waste Poly-ethylene Terephthalate (PET) bottle aggregates was investigated. Investigation was carried out on three groups of mortar specimens. One made with only Normal Portland cement (NPC) as binder, second made with NPC and GBFS together and, third made with NPC and FA together. The industrial wastes mentioned above were used as the replacement of cement on mass basis at the replacement ratio of 50%. The size of shredded PET granules used as aggregate for the preparation of mortar mixtures were between 0 and 4 mm. The waste lightweight PET aggregate (WPLA)–binder ratio (WPLA/b) was 0.60; the water–binder (w/b) ratios were determined as 0.45 and 0.50. The dry unit weight, compressive and flexural–tensile strengths, carbonation depths and drying shrinkage values were measured and presented. The results have shown that modifying GBFS had positive effects on the compressive strength and drying shrinkage values (after 90 days) of the WPLA mortars. However, FA substitution decreased compressive and flexural–tensile strengths and increased carbonation depths. Nevertheless a visible reduction occurred on the drying shrinkage values of FA modifying specimens more than cement specimens and GBFS modified specimens. The test results indicated that, GBFS has a potential of using as the replacement of cement on the WPLA mortars by taking into consideration the characteristics. But using FA as a binder at the replacement ratio of 50% did not improve the overall strength properties. Although it was thought that, using FA as binder at the replacement ratio of 50% for the aim of production WPLA concrete which has a specific strength, would provide advantages of economical and ecological aspects.     

Strength and drying shrinkage properties of self-compacting concretes incorporating multi-system blended mineral admixtures

Drying shrinkage can be a major reason for the deterioration of concrete structures. The contraction of the material is normally hindered by either internal or external restraints so that tensile stresses are induced. These stresses may exceed the tensile strength and cause concrete to crack. The present study investigated compressive strength and particularly drying shrinkage properties of self-compacting concretes containing binary, ternary, and quaternary blends of Portland cement, fly ash (FA), ground granulated blast furnace slag (GGBFS), silica fume (SF), and metakaolin (MK). For this purpose, a total of 65 self-compacting concrete (SCC) mixtures were prepared at two different water to binder ratios. It was observed that drying shrinkage lessened with the use of FA, GGBFS, and MK while incorporation of SF increased the drying shrinkage.     

Effect of blended cements produced with natural zeolite and industrial by-products on alkali-silica reaction and sulfate resistance of concrete

In this study, influence of blended cements produced with different types of pozzolans on alkali-silica reaction (ASR) and sulfate resistance of concrete was investigated. For this reason, natural zeolite (clinoptilolite), fly ash (FA), and ground granulated blast furnace slag (GBFS) were used in different types of blended cement production. According to the mechanical performance of these blended cements, ASR and sulfate resistance experiments were carried out to obtain the durability performance of these cements. The length changes and microstructure investigations of the mortar specimens with different types of blended cements showed that zeolite, FA, and GBFS had reduced ASR and sulfate damages when compared with ordinary CEM I 42.5 reference specimen.     

粉煤灰和引气剂对玻化微珠保温砂浆性能的影响

通过在玻化微珠保温砂浆中掺入不同掺量的粉煤灰和引气剂,系统研究粉煤灰和引气剂对玻化微珠保温砂浆稠度、湿表观密度、干表观密度、抗压强度、导热系数、线性收缩率的影响规律。结果表明:在单掺粉煤灰时,保温砂浆的稠度先增大后降低,而湿表观密度、干表观密度、抗压强度和导热系数均为先降低后增大,同时粉煤灰对砂浆收缩有一定的抑制作用。在粉煤灰和引气剂共掺时,考虑到保温砂浆综合性能,存在引气剂的最佳掺量值。掺入20kg/m3粉煤灰和0.1%引气剂的玻化微珠保温砂浆可以得到较好的性能。     

钢渣用作水泥混合材的试验探究

研究了钢渣与矿粉按1∶2、1∶1、2∶1、1∶0掺合的复合粉分别以25%、35%、50%、60%掺入水泥中,对水泥胶砂力学性能的影响,并采用XRD和SEM分析其水化产物。结果表明:随着钢渣掺量的增加,水泥胶砂强度降低,当钢渣掺量超过30%时,强度降低尤为明显,但所配制水泥的技术指标均符合GB/T 175—2007《通用硅酸盐水泥》的技术要求。较钢渣单掺,钢渣与矿粉复掺有利于水泥强度的发展,但大掺量钢渣(60%以上)造成水泥安定性不良。钢渣掺量控制在25%内可以作为混合材应用于水泥生产中。     

多孔混凝土基层的应力-应变特性

为进行多孔混凝土基层路面的结构设计,需研究其应力-应变特性.通过小梁试件三分点加荷试验及棱柱体试件轴心抗压试验,分别测试多孔混凝土的弯拉弹性模量与轴心抗压弹性模量.对试验结果进行回归分析,得出多孔混凝土弯拉弹性模量与弯拉强度、抗压弹性模量与轴心抗压强度之间分别符合相关性良好的幂指数关系,并据此得出多孔混凝土弯拉弹性模量与弯拉强度、抗压弹性模量与轴心抗压强度的对应关系表,作为其弹性模量的推荐值.     

模型再生混凝土单轴受压动态力学特性试验

试验设计了再生粗骨料取代率为100%的模型再生混凝土（MRC）、模型普通混凝土（MC）、再生粗骨料取代率55%的模型再生混凝土（MCP）和模型砂浆（MM）4种试件,在不同应变速率下进行单轴受压试验。研究表明：随着加载应变速率的提高,试件应力-应变曲线形状相似,峰值应力和弹性模量表现出增大的趋势,峰值应变的变化无明显规律;MRC、MC、MCP试件破坏时裂缝最先出现在界面区附近,然后逐渐发展直至贯通,随着应变速率的提高,裂缝较宽且开展更快,试件完全断裂成若干碎块;模型再生混凝土静态强度越低,峰值应力和弹性模量增长越大,动态效应越显著;再生粗骨料取代率为55%时,峰值应力和弹性模量增长最大;模型砂浆试件的动态效应最显著,模型普通混凝土和模型再生混凝土次之,且相差不大。     

高温后新Ⅲ级钢筋力学性能的试验研究

通过对37组共111根(?)16和(?)12新Ⅲ级钢筋高温后的力学性能试验,研究了经历不同受火温度和受火恒温时间 后的屈服强度、极限强度、弹性模量、延伸率和受拉应力-应变关系等力学性能的变化规律。试验表明。新Ⅲ级钢筋在经历 高温作用后,其屈服强度、极限强度和弹性模量在400℃以前变化不大,之后随所经历温度的升高而逐渐下降,降幅一般在 15％左右,实测的受拉应力-应变关系曲线,仍然出现明显的屈服台阶和强化段。根据试验结果,本文建议了高温后新Ⅲ 级钢筋屈服强度、极限强度、弹性模量、延伸率和受拉应力.应变全曲线计算公式。本文研究成果可作为火灾后混凝土结 构的损伤评估和非线性有限元全过程分析的依据。     

The effect of Persian Gulf tidal zone exposure on durability of mixes containing silica fume and blast furnace slag

In this research the performance of cement paste and concrete mixes incorporating 7% and 10% of silica fume (SF) as a cement replacement was investigated in three exposure conditions. The results showed that plain type II portland cement performed better than blended SF cement under cyclic wetting and drying conditions. Silica fume specimens under cyclic wetting and drying conditions in simulated seawater exhibited higher strength loss compared to plain type II portland cement where cured under potable water. In addition, the greater the silica fume amount used in the mixes, the more the capillary water absorption under tidal zone exposure or/and under wetting and drying simulation. Further, the ternary blended ground granulated blast furnace slag (GGBS) mix was the worst performing mix in all exposure conditions.     

Freeze–thaw resistance of blended cements containing calcined paper sludge

This work deals with the frost resistance of blended cements containing calcined paper sludge (source for metakaolin) as partial Portland cement replacements. Freeze–thaw tests were performed on blended cement mortars containing 0%, 10% and 20% waste paper sludge calcined at 650 °C for 2 h. Cement mortar specimens were exposed to freezing and thawing cycles until the relative dynamic modulus of elasticity fell below 60%. The performance of the cement mortars was assessed from measurements of weight, ultrasonic pulse velocity, compressive strength, mercury intrusion porosimetry and SEM. Failure of the control cement mortar occurred before 40 freeze/thaw cycles, while cement mortar containing 20% calcined paper sludge failed after 100 cycles. After 28 and 62 freezing and thawing cycles, cement blended with 10% and 20% calcined paper sludge exhibited a smaller reduction in compressive strength than the control cement.     

抹面抗裂砂浆的优化设计

针对普通抹面砂浆受冷热环境交替作用容易开裂的问题,研制了高柔性的抹面抗裂砂浆.通过正交试验,研究了橡胶粉、聚合物胶粉和聚丙烯纤维掺量对砂浆抗压强度、抗折强度、压折比、收缩率和弹性模量的影响.结果表明,橡胶粉、聚合物胶粉、聚丙烯纤维的加入使砂浆的弹性模量降低,柔韧性增加,抗裂性提高,另外,确定了柔性抹面砂浆的最佳配合比.     

Relationship between average pore diameter and chloride diffusivity in various concretes

Since concrete is a heterogeneous composite material which is composed of cement, aggregate, mineral admixture, and so on, the microstructure of concrete is very important to predict transport property associated with the durability of concrete. In this paper, 12 concrete specimens composed of six types of Portland and blended cements with water–binder ratios of 40% and 50% were manufactured to investigate the characteristics of capillary pores using mercury intrusion porosimetry technique and examine measurements of chloride diffusivity in concrete regard to electric potential. The average pore diameter of concretes decreased in the following order: (1) low heat cement, (2) ordinary Portland cement and sulfate resistant cement, (3) blended cement with 40% of slag, (4) blended cement with 60% of slag and, (5) ternary based cement. On the other hand, chloride diffusivity decreased in the following order: (1) low heat cement, (2) ordinary Portland cement and sulfate resistant cement, (4) blended cement with 40% of slag, (3) blended cement with 60% of slag and ternary based cement, indifferently from water–binder ratio. From the result of regression analysis, the chloride diffusivity increased with the average pore diameter presenting a very satisfactory correlation factor exceeding 0.91.     

国产超高强钢Q890高温力学性能试验

通过稳态拉伸试验法对国产超高强钢Q890在不同火灾高温条件下的力学性能进行了试验研究,得到高温下钢材的力学性能参数、应力-应变关系曲线和试验现象,并将所得试验结果与钢结构抗火设计规范及相关超高强钢研究文献中高温材料模型结果进行比较。分别采用多项式模型和钢材高温通用材料模型对试验结果进行数值拟合,建立高温下Q890钢力学性能参数的材料模型。结果表明:不同温度条件下的Q890钢试件在试验后有明显不同的外观特征,相应的应力-应变关系曲线基本形状差异较大;当受热温度低于500 ℃时,弹性模量和强度随温度升高逐步减小,断后伸长率变化不大;超过500 ℃后,弹性模量和强度下降速率明显加快,断后伸长率急剧增大;所建立的模型为研究Q890钢结构抗火性能及其计算方法提供理论基础。     

CRTSⅠ型CA砂浆动态受压损伤试验

在电子万能试验机上对现场取样的水泥乳化沥青砂浆(CA砂浆)试件在应变率1×10-5～1×10-2S-1下进行动态单轴抗压试验,分析了动态荷载下CA砂浆的抗压强度、弹性模量及临界应变随应变率的变化规律.结果表明:CA砂浆的抗压强度随应变率的增加而增大,CA砂浆的抗压强度、弹性模量及临界应变与应变率之间呈幂函数关系,并给出了抗压强度、弹性模量及临界应变受应变率影响的经验公式.以切线模量的退化来度量CA砂浆的损伤程度,分析了CA砂浆动态损伤槛值随应变率的变化规律:当加载到相同的应变时,应变率越低,CA砂浆的损伤程度越严重;随着应变率的增大,CA砂浆损伤应力槛值及损伤应变槛值均增大;当应变率较高时,应变率对损伤应力槛值与平均抗压强度的比值和损伤应变槛值与平均临界应变的比值影响不大.     

Thermal conductivity and compressive strength of concrete incorporation with mineral admixtures

In this study, the effect of silica fume (SF), class C fly ash (FA), blast furnace slag (BFS), SF+FA, SF+BFS, and FA+BFS on the thermal conductivity (TC) and compressive strength of concrete were investigated. Density decreased with the replacement of mineral admixtures at all levels of replacements. The maximum TC of 1.233 W/mK was observed with the samples containing plain cement. It decreased with the increase of SF, FA, BFS, SF+FA, SF+BFS, and FA+BFS. The maximum reduction was, 23%, observed at 30% FA. Compressive strength decreased with 3-day curing period for all mineral admixtures and at all levels of replacements. However, with increasing of curing period reductions decreased and for 7.5% SF, 15% SF, 15% BFS, 7.5% SF+7.5% FA, 7.5% SF+7.5% BFS replacement levels compressive strength increased at 28 days, 7- and 28-days, 120 days, 28- and 120 days, 28 days curing periods, respectively. Maximum compressive strength was observed at 15% BFS replacement at curing period of 120 days.