Effect of Lateritic Stone Aggregate and Coconut Husk Fiber on the Properties of Concrete

Natural stone aggregate forms the bulk volume of concrete and has contributed to the increased cost of concrete production. This has led to the search for alternate aggregates such as lateritic stone for concrete production. This paper investigates the engineering properties of concrete produced with lateritic aggregate (LA) as the coarse aggregate replacement and coconut husk fibre (CHF) as reinforcement. Natural stone aggregate was replaced by LA at 0%, 10%, 20%, 30%, 40%, and 50%, with 0.25% constant CHF by weight. A mix proportion of 1:1.5:3 with a water-cement ratio of 0.6 was used for producing concrete. A total of 162 specimens (90 cubes and 72 beams) were prepared and tested at the 7, 14, 21, and 28 days of curing. The highest compressive strength was 43.36 N/mm2 (10% LA replacement) as compared to the control of 41.51 N/mm2. The 10% LA replacement obtained the highest flexural strength of 5.35 N/mm2 as compared with the 5.29 N/mm2 for the control. The water absorption of the concrete increased from 2.8% (control) to 3.57% (50% replacement LA). Scanning electron microscopy (SEM) revealed micro gaps between CHF and LA concrete. The study, therefore, concludes that the use of LA and CHF positively influenced the strength properties of concrete. 10% LA replacement of coarse aggregate and 0.25% CHF is recommended to practitioners for use.

Effect of Recycled Coarse Aggregate on Concrete Compressive Strength

The effect of recycled coarse aggregate on concrete compressive strength was investigated based on the concrete skeleton theory. For this purpose, 30 mix proportions of concrete with target cube compressive strength ranging from 20 to 60 MPa were cast with normal coarse aggregate and recycled coarse aggregate from different strength parent concretes. Results of 28-d test show that the strength of different types of recycled aggregate affects the concrete strength obviously. The coarse aggregate added to mortar matrix plays a skeleton role and improves its compressive strength. The skeleton effect of coarse aggregate increases with the increasing strength of coarse aggregate, and normal coarse aggregate plays the highest, whereas the lowest concrete strength occurs when using the weak recycled coarse aggregate. There is a linear relationship between the concrete strength and the corresponding mortar matrix strength. Coarse aggregate skeleton formula is established, and values from experimental tests match the derived expressions.

Different Curing Systems on Mechanical Properties of Ultra-High Performance Concrete with Coarse Aggregate

High durability and high tensile strength makes ultra-high performance concrete( UHPC) an ideal material for bridges,while its early shrinkage in the construction of cast-in-situ mass concrete leads structure crack-easily,which restricts the application of UHPC in deck system. Whether reasonable amount of coarse aggregate can influence the strength of UHPC and improve the shrinkage performance or reduce the cost is still in doubt. Besides,in order to improve its constructability and workability, whether autoclaved curing system of UHPC can be changed remains to be further researched. In response to these circumstances, a systematic experimental study on the strength of UHPC mixed with coarse aggregate in different ratios has been presented in this paper. The three curing systems,namely standard curing,180-200 ℃/1. 1 MPa autoclaved curing,and hot water curing were tested to reveal the relationship between UHPC's properties and curing systems,and the UHPC ' s microstructure was also preliminarily studied by scanning electron microscope( SEM). The experimental research can draw the following conclusions. Under the condition of the same mix ratio, autoclaved curing guarantees the highest compressive strength,followed by hot water curing and standard curing. The compressive strength of concrete increases with the temperature in the range of 25 to 90 ℃ hot water curing,and high temperature in precuring period can speed up the strength development of UHPC,but the sequence of precuring period does not obviously affect the results. In 90 ℃ hot water and autoclaved curing,the strength is over 150 MPa,and it has little relation with gravel ratio. While the value increases first and then decreases in a lower temperature curing with the increasing of gravel amount,even only about 80 MPa at room temperature. The strength increases moderately along with the increase of the curing age by standard curing,especially in the initial stage.

Performance Degradation of the Repeated Recycled Aggregate Concrete with 70% Replacement of Three-generation Recycled Coarse Aggregate

The feasibility of using different generations recycled coarse aggregate（RCA） on structural concrete was fully evaluated by studying the performance of the recycled coarse aggregates and their corresponding concretes, the different generations of RCA were recycled by following the repeated mode of ‘concrete-waste concrete-coarse aggregate-concrete＇. Moreover, the focus was on ‘three generations＇ of repeated RCAs, the RCA was produced by crushing and regenerating the artificial accelerated degraded concrete, the process was designed to follow the nature degradation of the concrete with a coupling action of accelerated carbonation and bending load. The properties of x-generation（x=1, 2 or 3） of repeated RCA were systematically investigated and the compressive and splitting tensile strengths of relating structural concretes（with 70% replacement of x-generation of RCA） were studied accordingly. The results show a competent compressive and splitting tensile strength of 30 MPa at 28 th day of structural concretes with all generations of repeated RAC. And the gradual degraded performance of the repeated RCAs was observed with an increased numbers of repetition（1〉2〉3 generations）, the overall performances of all repeated RCAs fulfill the Class Ⅲ according to Chinese Standards GB25177-2010. Our gained insight demonstrates a feasibility of using at least 3 generations of repeated RCA for the production of normal structural concrete.

Finite Element Analysis on the Uniaxial Compressive Behavior of Concrete with Large-Size Recycled Coarse Aggregate

To model the concrete with complex internal structure of concrete with large sized aggregates the effect of internal structure on uniaxial compression behavior are studied.Large-sized recycled aggregates behave differently in the concrete matrix.To understand the influence on concrete matrix,a finite element model was developed to model recycled aggregate concrete composed of multiple randomly distributed irregular aggregates and cement mortar.The model was used to calculate the effect of large-size recycled coarse aggregate(LRCA)on the strength of recycled aggregate concrete and simulate the compressive strength of cubes and prisms.The factors such as the strength of new concrete,the strength of old concrete,the defective element content,the shape of LRCA,the incorporation ratio of LRCA and the size of LRCA that can affect the strength of concrete are analyzed in this paper.Results showed that the influence of various factors on concrete strength are in the following desend-ing order:(i)strength of newly poured concrete;(ii)original strength of recycled aggregates;and(iii)defects.It can be seen that the cracking of the phase material elements starts along the bonding zones between gravel and mortar or the new and old mortar,then spreads to mortar and finally to LRCA.The cracking tendency is most significant in LRCA,which means that the fracturing is related to the fracture of the LRCA.After evaluating the variations in strength and quality of the recycled concrete,the influences on concrete strength and quality were studied.The results showed that the proposed concrete model with LRCA was successfully applied to studying the uniaxial compressive behavior of concrete with large-size recycled coarse aggregate.

Effect of Partial Replacement of Coarse Aggregate with Electronic Waste Plastic in Light Weight Concrete

This study assessed the usefulness of the replacement of coarse aggregate partially with electronic waste(e-waste)plastic in lightweight concrete since developing countries have been challenged with management of e-waste as well as high cost of coarse aggregates for concrete production.Coarse aggregates were replaced with e-waste plastic in concrete at 5%,10%,15%,and 20% for a concrete class of C20.The particle size distribution of the e-waste plastic aggregates was determined as well as the slump,compressive strength,water absorption and bulk density of the concrete.Generally,the slump decreased as the e-waste increased.The compressive strengths decreased for the 5%and 10%replacement of coarse aggregates with e-waste but increased for the 15% and 20% replacement of coarse aggregate with e-waste.0% water absorption was obtained for the 15% and 20% e-waste content while the 10%e-waste concrete obtained 0.01% and the 5% e-waste obtaining of 0.013% after 28days of curing.The densities of 5%,10%,15% and 20% e-waste plastic content decreased as compared to the 0% e-waste plastic content.The values of compressive strength obtained showed that coarse aggregate replacements by e-waste plastic at 15% and 20% may be appropriate for lightweight concrete of class C20/25 since compressive strengths ranged between 16.09 Nmm^(-2) and 22.87 Nmm^(-2).This implies that partial replacement of coarse aggregate with e-waste plastic may be useful for lightweight concrete as well as helping in eradicating the environment of the menace of e-waste plastic.

机制砂再生粗骨料混凝土抗压强度试验研究

为探究机制砂原料种类和机制砂级配对机制砂再生混凝土抗压强度的影响,以细骨料类型(天然砂、石灰石机制砂、卵石机制砂)细骨料级配、水灰比为变量制作了30组机制砂再生混凝土立方体试块和15组天然砂再生混凝土立方体试块。结果表明:在石粉掺量10%时,机制砂再生混凝土抗压强度高于天然砂再生混凝土,且机制砂原料为石灰石的抗压强度高于卵石;机制砂各筛孔量占比分别为5%、7%、18%、25%、26%和14%时,机制砂再生粗骨料混凝土的抗压强度最高。研究表明:严格控制水灰比、颗粒级配可使机制砂再生混凝土达到设计强度、满足生产应用要求,采用机制砂替代天然砂制备再生骨料混凝土更有优势,是缓解天然砂资源短缺的可行途径之一。

粗集料对超高强混凝土徐变的影响

徐变是混凝土固有的时变特性,对混凝土结构和构件的受力及长期服役性能有着重大影响。以粗集料为切入点,研究粗集料的掺量、粗集料最大粒径以及粗集料与基体性质协调性等因素对超高强混凝土的力学性能和徐变性能的影响。结果表明:掺粗集料的超高强混凝土徐变明显小于不掺粗集料的混凝土,掺粗集料可有效降低超高强混凝土的徐变,但减小粗集料的最大粒径对徐变无明显抑制效果。此外,超高强混凝土并非强度越高徐变越小,其徐变的大小主要受超高强混凝土强度与弹性模量的协同发展程度的影响。通过修正FIB MC2010模型,建立了适用于超高强混凝土的徐变预测模型。

再生粗骨料取代率及粒径对混凝土抗压性能影响试验研究

为研究单轴受压情况下再生粗骨料粒径范围、取代率对再生混凝土抗压性能的影响规律,分别以粒径范围5~10、10~20和20~31.5 mm,以及取代率分别为0%、10%、30%和50%为参量设计制作再生混凝土棱柱体试件,并对其开展单轴抗压性能试验研究。结果表明:在取代率相同时,粒径范围为5~10 mm时再生混凝土的抗压强度及峰值应变均比粒径范围为10~20、20~31.5 mm时的大;在粒径范围相同情况下,随取代率增大,再生混凝土抗压强度呈现出逐渐减小的变化趋势,而峰值应变则呈现出逐渐增大的变化趋势。根据试验数据,得出了再生混凝土抗压强度和峰值应变的函数关系式。

橡胶粗细集料含量对FRP约束橡胶混凝土应力-应变关系的影响

为研究橡胶粗细集料体积分数对纤维增强复合材料(fiber reinforced polymer, FRP)约束橡胶混凝土应力-应变关系的影响,提出了橡胶粗细集料体积替换率的概念,并通过收集已发表文献的110组应力-应变关系试验曲线,分析了橡胶粗细集料体积替换率对FRP约束不同截面橡胶混凝土柱应力-应变关系关键参数的影响,基于分析结果建立了FRP约束橡胶混凝土的应力-应变关系模型和抗压强度模型,两个模型中均考虑了橡胶粗细集料体积替换率和橡胶混凝土截面形状的影响.模型评估结果表明:随着橡胶粗细集料体积替换率、FRP约束应力比和截面倒角半径比的增加,FRP约束橡胶混凝土的抗压强度均呈增大的趋势;建立的抗压强度模型可准确预测橡胶颗粒取代部分细集料或粗细集料的FRP约束橡胶混凝土抗压强度,平均误差仅为1.03;建立的应力-应变关系模型能够较好预测FRP约束橡胶混凝土的应力-应变关系曲线变化.

针片状颗粒对高强混凝土性能的影响研究

从粗骨料针片状颗粒角度出发,研究其含量和粒径对高强混凝土性能的影响。选取掺加5%、15%和25%针片状颗粒含量的粗骨料配制混凝土,对混凝土的工作性能、力学性能和耐久性能进行试验研究;选取5~10 mm、10~16 mm和16~20 mm共三种粒径区间的针片状颗粒,探究粒径大小对混凝土性能的影响规律。结果表明:针片状颗粒含量增加,高强混凝土和易性和泵送性能变差,混凝土抗压强度降低,混凝土收缩增大,且对高强混凝土耐久性能不利;混凝土拌合物坍落度和扩展度、硬化混凝土各龄期抗压强度均随着粗骨料中针片状颗粒粒径增大而降低;综合考虑针片状颗粒对高强混凝土性能影响规律,建议控制针片状颗粒含量不超过5%;同时,在计算针片状颗粒含量时,需在标准计算方法基础上按不同粒径针片状颗粒分别乘以其对应的影响系数进行修正,以实现对粗骨料粒形更好的控制。

粗骨料取代率对机制砂再生混凝土高温性能的影响

为探究不同粗骨料取代率对机制砂再生混凝土(RCM)高温性能的影响,以不同粗骨料取代率(0%、20%、40%、60%、80%、100%,质量分数)制备RCM并研究其单面受高温后的表面形貌、质量损失率、抗压强度、荷载变形曲线及微观形貌。结果表明,粗骨料取代率在40%~60%时,在低于600℃的高温试验下RCM表现良好。当温度在200℃时,各组试块表面形貌变化不大,质量损失率较小,抗压强度略微上升;当温度在400℃时,各组试块表面开始出现裂缝,质量损失率为4.35%~6.47%,抗压强度开始下降,此时粗骨料取代率影响不大;当温度达到600℃时,表面形貌变化明显,质量损失率上升到6.42%~8.70%,抗压强度最终降低到基准强度的80%左右,此时粗骨料取代率在40%~60%的试块表现良好;当温度达到800℃时,各组试块表面形貌变化进一步加剧,粗骨料取代率大于60%的试块受影响非常明显,同时各类性能参数表明混凝土已完全丧失工作性能。

机制砂全再生粗骨料混凝土的力学性能

为探究骨料类型、水灰比与石粉含量对机制砂全再生粗骨料混凝土力学性能的影响,制备了不同石粉质量分数(5%、10%和15%)和不同水灰比(0.50、0.37和0.32)的全再生骨料混凝土试件.以72个立方体试件用于抗压强度试验,72个圆柱体试件用于弹性模量试验.结果表明,合理的石粉含量能有效提高再生骨料混凝土的力学性能,但在不同的水灰比下,最佳石粉含量存在差异;当水灰比和石粉含量双因素交互作用时,水灰比为0.32、石粉质量分数为15%的再生混凝土力学性能达到最优.构建了机制砂再生粗骨料混凝土抗压强度、弹性模量与水灰比、石粉含量的关系模型,计算结果的标准差与离散系数均不超过5%,模型精度良好.研究成果可为提高再生骨料混凝土力学性能及其工程应用提供理论依据.

基于GA-BP神经网络的粗骨料UHPC的抗压强度预测

为实现对粗骨料UHPC的抗压强度的预测和配合比设计方法的优化,搜集了国内外文献中168组粗骨料UHPC配合比和标准养护28 d抗压强度实测值,给出了各材料组分和抗压强度频数分布,并基于灰色关联分析法分析了各材料组分与抗压强度的关联关系,通过神经网络参数分析,建立了基于遗传算法的前馈神经网络,相比普通的BP神经网络具有更好的预测精度和泛化能力。最后基于建立的GA-BP神经网络给出了不同强度等级粗骨料UHPC配合比设计中粗骨料/胶凝材料、钢纤维体积掺量、砂胶比的建议取值范围。

粗骨料粒径对珊瑚混凝土力学性能的影响

为了探究粗骨料粒径对珊瑚混凝土的静态力学性性能,采用RMT-150实验机结合材料力学相关知识,对连续级配粗骨料粒径为5~16mm(J0)及单一级配粗骨料粒径为5~10mm(J1)、10~16mm(J2)、16~20mm(J3)和20~25mm(J4)进行静态抗压抗拉试验,并且对比分析实验结果,探究不同粗骨料粒径珊瑚混凝土的力学性能。研究结果表明:粗骨料粒径为5~10mm的时候珊瑚混凝土的抗压抗拉强度达到最佳,随着骨料粒径的增大,珊瑚混凝土的抗压抗拉强度呈现先增加后减小的趋势。适当的粗骨料粒径能够提升粗骨料混凝土的静态抗压抗拉强度。

再生陶瓷混凝土抗压强度及弹性模量试验研究

【目的】为研究不同再生陶瓷骨料类型和取代率对混凝土抗压强度和弹性模量的影响,利用再生陶瓷细骨料以0、10%、20%、30%、40%、50%、60%、70%、80%、90%和100%取代率等质量替换天然河砂制作再生陶瓷细骨料混凝土(CRFC)。【方法】在再生陶瓷细骨料全取代(100%)天然细骨料的基础上,采用再生陶瓷粗骨料等质量替换天然碎石制作再生陶瓷粗细骨料混凝土(CRC),研究CRFC和CRC的物理性能和力学性能,分析废弃墙地砖陶瓷作为混凝土再生骨料的可行性。【结果】研究表明:采用再生陶瓷细骨料取代天然细骨料配制的CRFC在和易性、抗压强度和弹性模量等性能方面与普通混凝土相差不大;CRC的抗压强度和弹性模量随再生陶瓷粗骨料取代率的增加而显著降低。【结论】废弃陶瓷砖可以作为粗、细骨料用于制备混凝土。采用再生陶瓷粗骨料时需要根据其吸水率加入附加用水以确保混凝土拌合物的和易性;界面过渡区的粘结强度和粗骨料类型是分别影响CRFC和CRC破坏形态的主要因素;再生陶瓷细骨料全部取代天然细骨料时,建议再生陶瓷粗骨料取代率小于50%。

氧化石墨烯对再生混凝土抗压强度的影响

研究了氧化石墨烯(GO)的掺量(0、0.042%、0.063%、0.084%、0.105%)对不同再生粗骨料取代率(0、40%、60%、80%、100%)再生混凝土试件抗压强度的影响,并拟合得到了掺GO再生混凝土的抗压强度与再生粗骨料取代率之间的关系表达式。结果表明:随着GO掺量的增加,试件的抗压强度呈先增大后减小的趋势,且当GO的掺量为0.063%时,试件的抗压强度达到最高;随着再生粗骨料取代率的增加,试件的抗压强度降低;ExpDec3指数函数可较为准确地表达掺GO再生混凝土的抗压强度与再生粗骨料取代率之间的关系。

水射流回收废弃混凝土的再利用性能试验研究

废弃混凝土的妥善处置是城镇固体垃圾处理的重要议题,将废弃混凝土进行有效回收并作为再生混凝土再利用被认为是提高建筑垃圾资源化率的有效策略。本研究将水射流引入旧建筑物拆除和废弃混凝土回收领域,研究了水射流拆除旧建筑物回收再生混凝土构件和水射流致裂混凝土回收再生粗骨料的应用潜力,分析了断面粗糙度对于新老混凝土界面连接性能的影响。结果表明:水射流拆除后再生混凝土的剩余强度保留在91%到98%,表明水射流拆除对于混凝土性能的影响是微不足道的。再生混凝土的断面粗糙度保持在1.10~1.31,水射流拆除造成的粗糙表面对于新老混凝土界面的粘结非常有利。水射流冲击下,粗骨料和砂浆能够有效分离,再生粗骨料的附着砂浆含量低于10%。

再生混凝土力学性能研究现状与挑战

下文介绍了再生混凝土基本概念及其在建筑领域的重要性,并对再生混凝土抗压强度、抗折强度、耐久性等性能进行凝练,使其与普通混凝土进行比较。同时,还对再生混凝土的制造等方面提出改进方法,使其力学性能得到提升,以确保其在建筑结构中的安全可靠性;最后对其未来发展趋势和挑战进行讨论,认为再生混凝土在推广应用过程中具有广阔市场前景和应用潜力。

碳化再生骨料对混凝土力学性能的影响研究

为研究碳化再生粗骨料的性能及其对再生混凝土力学性能的影响,采用加速碳化技术制备碳化再生粗骨料,碳化室的CO_(2)浓度为100%,压强分别为1 Bar和10 Bar。采用再生粗骨料替代率为0%、25%、50%、75%和100%制备混凝土。测试再生粗骨料的物理性能和混凝土的抗压强度、静弹性模量和抗折强度。结果表明:(1)在进行加速碳化处理后,再生粗骨料的物理性能和力学性能均得到了改善;(2)与非碳化的再生粗骨料混凝土相比,碳化再生粗骨料混凝土的抗压强度和抗折强度均得到了明显的提高;(3)与天然骨料混凝土相比,碳化骨料替代率在50%以下时,混凝土的抗压强度和抗折强度没有显著降低。