橡胶改性及其对橡胶水泥基质材料性能的影响

本文基于提高橡胶-水泥基质材料的力学性质的目的,对橡胶进行磺化-脲化改性.采用水接触角、红外光谱、粘接强度、抗压抗冲击强度等微观宏观测试技术考查了橡胶改性对橡胶水泥基质材料性能的影响.结果表明:橡胶氧化-脲化改性后,在橡胶表面引入了大量羰基、酰胺基等极性亲水性基团,使橡胶表面的浸润类型由憎水性质变为了亲水性质,大大增加了橡胶与水泥基体的界面相互作用,使橡胶与水泥浆体的粘接强度提高了33.4%.橡胶改性对减缓橡胶水泥基质材料的抗压强度降低有确定的效果,但是这种效果在橡胶水泥混凝土中比在水泥砂浆中更突出.橡胶掺量为细集料的30%或以下时,氧化-脲化改性的橡胶混凝土的抗压强度能够达到30 MPa以上,可以满足中等强度混凝土的要求.     

Influence of amount of recycled coarse aggregates and production process on properties of recycled aggregate concrete

In this study recycled coarse aggregates obtained by crushed concrete were used for concrete production. Four different recycled aggregate concretes were produced; made with 0%, 25%, 50% and 100% of recycled coarse aggregates, respectively. The mix proportions of the four concretes were designed in order to achieve the same compressive strengths. Recycled aggregates were used in wet condition, but not saturated, to control their fresh concrete properties, effective w/c ratio and lower strength variability. The necessity to produce recycled aggregate concrete with low-medium compressive strength was verified due to the requirement of the volume of cement. The influence of the order of materials used in concrete production (made with recycled aggregates) with respect to improving its splitting tensile strength was analysed. The lower modulus of elasticity of recycled coarse aggregate concretes with respect to conventional concretes was measured verifying the numeral models proposed by several researchers.     

Mechanical properties of polymer-modified lightweight aggregate concrete

This paper deals with the properties of styrene-butadiene rubber (SBR)-modified lightweight aggregate concretes (LWACs) for thin precast components, made with two Brazilian lightweight aggregates (LWAs). Properties in the fresh state, compressive strength, splitting tensile strength, flexural strength, and water absorption of LWACs were tested. The 7-day compressive strength and the dry concrete density vary from 39.7 to 51.9 MPa and from 1460 to 1605 kg/m³, respectively. The inclusion of SBR latex in LWACs decreases the water-(cement+silica fume) [W/(C+S)] ratio and water absorption and increases the splitting tensile and flexural strengths. The results of this pilot study suggest that there are possibilities of producing thin precast components using SBR-modified LWACs with Brazilian LWAs.     

废旧橡胶粒径对水泥砂浆和混凝土强度影响研究

目前关于废旧橡胶颗粒粒径对水泥混凝土强度的影响规律研究结果存在相互矛盾的情况,关于其对水泥砂浆强度的影响规律鲜有报道。本文系统研究了5目和100目两种粒径废旧橡胶颗粒对砂浆和混凝土抗压强度的影响规律。结果表明,相同取代量下,5目橡胶砂浆抗压强度总是高于100目橡胶砂浆。而对于橡胶混凝土,在较低取代量下,100目橡胶混凝土抗压强度高于5目橡胶混凝土,当达到一定取代量后,100目橡胶混凝土抗压强度反而低于5目橡胶混凝土,存在一个转变取代量,对于不同龄期强度,转变取代量不同。对于28 d强度,当取代量大于50%后,100目和5目橡胶混凝土抗压强度相差不明显。     

Effect of aggregate and water to cement ratio on concrete properties at elevated temperature

Properties of concrete during and after fire exposure are of significant importance for serviceability and rehabilitation of buildings. This article presents an experimental investigation on the effects of elevated temperature on physical and mechanical properties of concrete made using two types of locally available coarse aggregates (crushed and wadi aggregates) and water‐to‐cement (w/c) ratios of 0.50 and 0.70. Temperature range from 200 °C to 1000 °C was used with intervals of 200 °C. Test results indicate that the weight of concrete reduced with increase in temperature. This reduction was quite sharp beyond 800 °C. Minor spalling was observed in concrete with Wadi aggregates at temperatures beyond 800 °C. The results also reveal that relative strength of concrete decreased as exposure temperature increased. The effect of high temperatures on the strength of concrete was more pronounced in concrete with Wadi aggregates. w/c ratio had insignificant effect on weight loss after exposure to elevated temperatures, but it increased the rate of strength degradation irrespective of aggregate type used. Comparison of results with Eurocode (EC‐2) and American Concrete Institute (ACI) standards indicate that the concrete with both aggregate types can satisfy the limits of siliceous aggregates set by ACI, but concrete made with Wadi aggregates with w/c ratio of 0.50 failed to satisfy limits of EC‐2. Copyright © 2015 John Wiley & Sons, Ltd.     

再生骨料和橡胶颗粒对透水混凝土性能的影响

以C20透水混凝土为设计基准,再生骨料和橡胶颗粒掺量为影响因素,通过测定透水混凝土的连通孔隙率、透水系数、28 d抗压强度、劈裂抗拉强度及弹性模量等性能指标,研究再生骨料和橡胶颗粒对透水混凝土基本性能的影响规律;同时,采用拟合回归和综合对比的方法建立透水混凝土连通孔隙率与透水系数、劈裂抗拉强度及弹性模量与28 d抗压强度之间的关系模型.     

不同强度废旧混凝土水泥稳定再生材料路用性能研究

为了研究废旧混凝土强度与再生集料性能及水泥稳定再生基层材料的力学及耐久性能之间的影响规律,采用钻芯法对废旧桥梁T梁、立柱、废旧路面混凝土不同结构部位取样进行抗压强度试验,得出废旧混凝土的强度推定值,分别为25.8 MPa、37.4 MPa、58.1 MPa。对3种不同强度废旧混凝土再生集料的性能进行对比,并分析了不同强度废旧混凝土对再生集料性能及水泥稳定再生材料力学和耐久性能的影响。结果表明:废旧混凝土强度增加,再生集料的压碎值、针片状含量、吸水率减小,塑限指数及相对表观密度增大;废旧T梁、立柱、路面混凝土水泥稳定再生材料最佳含水率及最大干密度分别近似的呈线性减小和增大的趋势;同时,无侧限抗压强度、劈裂强度、抗压回弹模量、抗冲刷性能均表现增大的变化规律,但干缩性能减弱。废旧混凝土强度增加能有效提高水泥稳定再生材料的路用性能。     

废瓷砖再生骨料对砂浆及砼性能的影响

利用废弃瓷砖制备再生粗、细骨料以取代天然砂石,研究了废瓷砖再生骨料对砂浆、混凝土性能的影响;并通过劈裂实验及抗折实验,对比分析了再生骨料、天然碎石与水泥石的界面粘结性能.结果表明:在相同配比条件下,与天然砂石集料相比,废瓷砖再生骨料有利于提高砂浆、混凝土的强度,减小干缩率,但会导致工作性变差.在相同龄期条件下,不同类型骨料-水泥石的界面粘结强度均随水灰比的降低而增大.在相同水灰比条件下,废瓷砖再生骨料-水泥石界面28 d劈裂强度、抗折强度均较碎石-水泥石界面的要大,表明再生骨料-水泥石界面粘结性能更好.     

无机聚合物橡胶混凝土基本力学性能试验研究

无机聚合物和橡胶粉作为新型节能环保材料,一直是工程应用研究的热点问题。本文利用2～4 mm的橡胶颗粒按等体积代替细骨料的方式掺入无机聚合物混凝土中,配制出不同橡胶掺量（0％、5％、10％、15％、20％）的无机聚合物橡胶混凝土。根据GB／T 50081-2002《普通混凝土力学性能试验方法标准》对无机聚合物橡胶混凝土的基本力学性能进行系统的试验。研究结果表明：相对于基准混凝土,橡胶掺量5％～20％的无机聚合物橡胶混凝土的立方体抗压强度下降了9．5％～35．7％;橡胶掺量10％～20％的无机聚合物橡胶混凝土的劈裂抗拉强度下降了9．9％～18．2％,轴心抗压强度下降了20．2％～35．4％,弹性模量下降了3．2％～7．8％;无机聚合物橡胶混凝土早期强度高于普通橡胶混凝土,其中,7 d相对强度高出11．5％;随着橡胶掺量的增加,无机聚合物橡胶混凝土的拉压比增加,强度比基本不变;无机聚合物橡胶混凝土的抗裂性能、变形能力随着橡胶掺量的增加而增强。     

Thermal and residual mechanical profile of recycled aggregate concrete prepared with carbonated concrete aggregates after exposure to elevated temperatures

Thermal and residual mechanical performance of recycled aggregate concrete (RAC) prepared with recycled concrete aggregates (RCAs) after exposure to high temperatures has so far received less attention than that of conventional concrete prepared with natural aggregates (NAs). This study experimentally investigated thermal and residual mechanical performance of RAC prepared with different replacement percentages of non‐carbonated and carbonated RCAs after exposure to high temperatures. The residual mechanical properties, including compressive strength, modulus of elasticity, and peak strain at the maximum strength, were measured for evaluating the fire resistance of RAC. The experimental results showed that although the fire‐resistant ability of natural granite aggregates was high, thermal deterioration of the conventional concrete after exposure to 600°C, presented by thermal induced mesocracks, was more serious than that of RAC due to thermal incompatibility between NAs and mortar. Using the carbonated RCAs can reduce the width of thermal mesocrack in RAC. The residual mechanical properties of RAC after exposure to 600°C can be obviously improved by incorporating 20% to 40% of the carbonated RCAs. For the RAC made with the 100% carbonated RCAs, the ratio of residual to initial compressive strength after exposure to above 500°C was even higher than that of the conventional concrete.     

Scrap tire/aggregate composite: Composition and primary characterizations for pavement material

A new type of pavement material using scrap rubber, the so-called elastic and permeable pavement material (EPPM), was proposed in this study. EPPM is a new material to overcome water permeability and brittleness, which are defects of the conventional rubber asphalt and cement concrete, respectively. Those problems could be solved by introduction of grounded scrap rubber and structural design of EPPM. Results showed that key factors affecting the compressive strength and the water permeability of EPPM were the size of grounded scrap rubber and aggregate, the amounts and property of the binder. The optimum level of binder was about 8 wt%. The compressive strength and water permeability of EPPM were 1.1 and 116 times higher than those of conventional porous cement concrete, respectively.     

基于可压缩堆积模型的透水混凝土配合比设计

基于可压缩堆积模型,以全孔隙率为设计指标,提出了一种考虑成型过程和集料级配影响的透水混凝土配合比设计方法.该方法首先根据可压缩堆积模型挑选出干堆积密实度较高的级配集料,引入反映成型过程影响的比例因子λ建立了集料在透水混凝土中的堆积密实度与其干堆积密实度之间的关系,进而确定出单位体积透水混凝土的集料用量;然后根据集料用量和水灰比,计算得到透水混凝土的水泥浆体体积和水泥用量.对依据该方法设计的透水混凝土性能验证试验表明,实测全孔隙率与设计全孔隙率非常吻合,达到预设目标;透水混凝土强度随小粒径集料体积分数的变化趋势与集料干堆积密实度的相近,但是并非干堆积密实越高则强度越高,强度还受到集料粒径的影响.     

不同因素对长龄期混凝土抗压强度的影响*

基于有交互作用的四因素二水平正交表,成型了不同配合比的混凝土试块,探讨了活性掺合料种类、水泥强度、减水剂种类、细骨料种类,以及其交互作用对混凝土抗压强度的影响。结果表明：活性掺合料种类是四个因素中对90~360 d混凝土抗压强度影响最大的因素;90~360 d内,活性掺合料和水泥的交互作用一直影响着混凝土抗压强度,并且其影响程度随着龄期的延长先增大后减小,180 d时的影响程度达到最大值;细骨料种类对90~360 d混凝土抗压强度的影响可以忽略不计。     

Properties of concrete made with recycled aggregate from partially hydrated old concrete

Concrete having a 28-day compressive strength of 28 MPa was crushed at ages 1, 3 and 28 days to serve as a source of aggregate for new concretes, simulating the situation prevailing in precast concrete plants. The properties of the recycled aggregate and of the new concrete made from it, with nearly 100% of aggregate replacement, were tested.Significant differences were observed between the properties of the recycled aggregates of various particle size groups, while the crushing age had almost no effect. The properties of the concrete made with recycled aggregates were inferior to those of concrete made with virgin aggregates. Effects of crushing age were moderate: concrete made with aggregates crushed at age 3 days exhibited better properties than those made with aggregates of the other crushing ages, when a strong cement matrix was used. An opposite trend was seen when a weaker cement matrix was used. Some latent cementing capacity was seen in the recycled aggregates crushed at an early age.     

同掺再生粗细骨料混凝土的力学与耐久性能研究

为了探讨同时掺入大掺量再生粗骨料和细骨料制备C40及以上强度等级再生混凝土的可行性,在C45天然骨料混凝土配合比的基础上,采用II类再生粗骨料、I类再生细骨料,以同掺再生粗细骨料质量替代率为25%、50%、75%、100%配制了4组再生混凝土,研究了再生粗细骨料替代率对再生混凝土基本力学性能和耐久性能的影响规律。结果表明:当同掺再生粗细骨料的替代率为25%时,混凝土的力学性能下降很小,替代率为50%、75%的混凝土的抗压强度分别达到C45、C40等级,替代率100%的全再生粗细骨料混凝土的28 d抗压、劈拉、轴压强度和弹性模量等力学性能指标较天然骨料混凝土降低12.0%~23.2%,并达到C35抗压强度等级。增加再生粗细骨料的替代率会降低混凝土的耐久性,但即使是全再生粗细骨料混凝土仍可获得高的耐久性,其抗碳化性能、抗氯离子渗透性、抗冻性能分别达到T-IV、RCM-IV和F300等级,说明在混凝土中同时掺用50%及以上再生粗细骨料配制C40及以上强度等级的再生混凝土是可行的。     

Properties of rubberized concretes containing silica fume

A test program was carried out to develop information about the mechanical properties of rubberized concretes with and without silica fume. Two types of tire rubber, crumb rubber and tire chips, were used as fine and coarse aggregate, respectively, in the production of rubberized concrete mixtures which were obtained by partially replacing the aggregate with rubber. Six designated rubber contents varying from 2.5% to 50% by total aggregate volume were used. The concretes with silica fume were produced by partial substitution of cement with silica fume at varying amounts of 5–20%. Totally, 70 concrete mixtures were cast and tested for compressive and splitting tensile strengths, and static modulus of elasticity in accordance to ASTM standards. The design strength level ranging from 54 to 86 MPa was achieved using water–cementitious material (w/cm) ratios of 0.60 and 0.40. Test results indicated that there was a large reduction in the strength and modulus values with the increase in rubber content. However, the addition of silica fume into the matrix improved the mechanical properties of the rubberized concretes and diminished the rate of strength loss. Results also revealed that a rubber content of as high as 25% by total aggregate volume might be practically used to produce rubberized concretes with compressive strength of 16–32 MPa.     

粗集料嵌锁型高强高性能混凝土的制备与性能

为了保证塑性混凝土的必要的工作性和均匀性,通常的新拌混凝土的粗集料体积分数控制在比较低的水平,尽管集料间也有少量嵌锁,粗集料大体上悬浮在砂浆之中.采用作者发明的抛填骨料混凝土工艺即在混凝土施工过程中均匀抛入一定体积率的粗集料,仅用440 kg/m3胶凝材料制备了抗压强度为94MPa的混凝土.研究表明:抛填骨料工艺能制备骨料之间相互嵌锁的混凝土,随着抛填骨料对初始混凝土的体积置换率10%到20%的增加,混凝土的强度和弹性模量在体积置换率20%时达到最大,随后有所降低;混凝土的氯离子渗透系数和干缩系数随着置换率的增加而降低.抛填集料对混凝土的取代不仅提高了混凝土的强度而且改善了混凝土的其他性能.     

Fire resistance of geopolymer concrete produced from Elazığ ferrochrome slag

This paper presents the effect of elevated temperatures up to 700 °C on compressive strength and water absorption of two alkali‐activated aluminosilicate composites (one of them is river sand aggregate geopolymer concrete; the other one is crushed sand aggregate geopolymer concrete) and ordinary Portland cement based concretes. To obtain binding geopolymer material, Elaz?? ferrochrome slag was ground as fine as cement, and then it was alkali activated with chemical (NaOH and Na₂SiO₃). Geopolymer concrete samples were produced by mixing this binding geopolymer material with aggregates. At each target temperature, concrete samples were exposed to fire for the duration of 1 h. Fire resistance and water absorption of geopolymer and ordinary Portland cement concrete samples were determined experimentally. Experimental results indicated that compressive strength of geopolymer concrete samples increased at 100 °C and 300 °C temperatures when compared with unexposed samples. In geopolymer concrete samples, the highest compressive strength was obtained from river aggregates ones at 300 °C with 37.06 MPa. Water absorption of geopolymer concrete samples increased at 700 °C temperature when compared with unexposed samples. However, a slight decrease in water absorption of concrete samples was observed up to 300 °C when compared with unexposed samples. SEM and X‐ray diffraction tests were also carried out to investigate microstructure and mineralogical changes during thermal exposure. Copyright © 2016 John Wiley & Sons, Ltd.     

不同应变速率下橡胶混凝土损伤本构模型

为获得低应变速率下橡胶混凝土的力学性能,本文进行了不同应变速率下橡胶混凝土的轴压试验,分析了混凝土细骨料的橡胶颗粒体积替换率和应变速率对橡胶混凝土力学性能的影响规律。结果表明,随着应变速率的增加,橡胶混凝土的应力-应变关系曲线和抗压强度均呈现增大的趋势,橡胶混凝土初始损伤值呈现递减的趋势,但应变速率对橡胶混凝土的弹性模量影响不显著。当应变速率从3.3×10^-5/s增加至3.3×10^-3/s时,橡胶体积替换率为0%、20%和30%的橡胶混凝土抗压强度分别增加了31%、24%、10%。当橡胶体积替换率率从0%变化到30%时,承受应变速率为3.3×10^-5/s、3.3×10^-4/s和3.3×10^-3/s的橡胶混凝土抗压强度分别减少了17%、15%、30%;橡胶混凝土的耗能随着加载速率的增加,整体呈现增大的趋势。最后基于试验数据建立了不同应变率下橡胶混凝土的损伤本构关系模型,并采用试验数据验证了新建立模型的准确性。     

Physicomechanical properties of irradiated SBR latex polymer‐modified cement mortar composites

This study investigated the effect of styrene–butadiene‐rubber (SBR) latex/cement ratio as well as γ‐irradiation dose on physicomechanical properties of cement mortar. Specimens were prepared with a different SBR/cement mass ratio of 2.5, 5, 10, 15, and 20. Two curing methods were used: wet cure and dry cure. The best specimens were irradiated to doses of 10, 30, and 50 kGy. The compressive strength, total porosity, and bulk density were studied. The result indicated that the compressive strength, total porosity, and the bulk densities of the composites decrease with increase in the polymer cement ratios. In addition, it was observed that the compressive strength of irradiated polymer‐modified cement mortar composites was improved with the increase in the γ‐irradiation dose, and the compressive strength of mix‐cured samples was higher than those wet‐cured samples at any irradiation dose. X‐ray diffraction, thermogravimetric analysis, acid attack, and microstructure of SBR‐modified cement mortar were characterized. J. VINYL ADDIT. TECHNOL., 26:144–154, 2020. © 2019 Society of Plastics Engineers