Influence of Selected Curing Techniques on Compressive Strength of Concrete From Palm Kernel Shell Ash and Ordinary Portland Cement

This paper discusses the findings of an experimental study on the effect of various curing procedures on the compressive strength of concrete pro­duced by partially substituting portland cement with Palm Kernel Shell Ash(PKSA).Palm kernel shell ash was utilized in a 1:2:4 mix ratio as a partial substitute for ordinary Portland cement(OPC)at percentage levels of 0%,10%,and 15%.River sand with particles passing a 4.75 mm BS sieve was used,as well as crushed aggregate with a maximum size of 20 mm,and palm kernel shell ash with particles passing a 212μm sieve.The compressive strength of the test cubes(150 mm × 150 mm × 150 mm)was determined after 7,28,and 56 days of curing.The results demonstrated that test cubes containing Palm kernel shell ash developed strength over a longer curing period than ordinary Portland cement concrete samples and that the strength changes depending on the amount of PKSA in the cube samples.The findings showed that at 28 days,test cubes with 5%,10%,and 15%PKSA content in all curing procedures utilized obtained a greater compressive strength.Curing by immersion produced the highest compres­sive strength in all replacement level while the concrete cured by sprinkling and spraying gives a lower strength in all replacement level.

Determination of the Compressive Strength of Concrete from Binary Cement and Ternary Aggregates

One of the most active fields of research embraced by many disciplines, including civil engineering, is material reuse. It is known that ceramics wastes from various construction and demolition sites and manufacturing processes are dumped away into the environment, resulting in the pollution that threatens both agriculture and public health. Therefore, the utilization of ceramic waste in construction industries would help to protect the environment from such pollutions. This paper presents the results of an experimental analysis of the effects of partial replacement of coarse aggregates, fine aggregates, and ordinary Portland cement with the ceramic waste, at percentage levels of 0%, 5%, 10%, and 20%;and the assessment of the strength property of the concrete produced with optimum combination of the constituents. Compressive strengths of this concrete were determined at 7, 28, and 56 days of curing using 150 × 150 × 150 mm cube specimens. Test results showed that the compressive strength of the concrete decreased as the content of ceramic waste present in the concrete increased. Thus, concrete produced from the partial replacement of ordinary Portland cement with ground ceramics gave compressive strengths of 16.6 N/mm2 and 13.4 N/mm2 at 5% and 20% replacement levels respectively. Similarly, the compressive strengths of concrete from the partial replacement of sand with fine ceramics were 13.8 N/mm2 and 10.9 N/mm2 for 5% and 20% replacements respectively. For 5% and 20% replacement levels of granite with crushed ceramics in concrete gave a compressive strength of 11.6 N/mm2 and 9.7 N/mm2, respectively. For concrete derived from the partial replacement of stone dust with fine ceramics, the compressive strengths were 19.6 N/mm2 and 18.10 N/mm2 respectively for 5% and 20%. For concrete produced from the partial replacement of bush gravel with crushed ceramics, the compressive strengths obtained were 10.9 N/mm2 and 8.98 N/mm2 respectively for 5% and 20% replacements. Finally, the concrete derived from the optimal combination of binary cement, ternary fine, and coarse aggregate had a compressive strength of 22.20 N/mm2 which is higher than the compressive strength of the control mixture at 18.10 N/mm2. The result of the ANOVA carried out showed that the compressive strength obtained for each partial replacement of different components is statistically significant at 5%, i.e. the change in the compressive strength of the concrete produced is due to the presence of ceramic waste.

Colloidal gas aphron(CGA) based foam cement system

To solve the problems such as high denstiy,foam instability,low compressive strength,high porosity and poor durability associated with conventional foam cements,a novel colloidal gas aphron(CGA)based foam cement system was investigated and tested for properties.CGA is used in a base slurry as the foam component and the recipe was optimized with hollow sphere and micro-silica in terms of particle size distribution(PSD).Porosity,permeability,strength,brittleness,elasticity,free water content,foam stability and density tests on the CGA based foam cement system were carried out to evaluate the performance of the system.According to the experiment results,at the foam proportion of 10%,the cement density was reduced to 1040 kg/m3,and stable microfoam net structure not significantly affected by high temperature and high pressure was formed in the cement system.The optimal CGA based foam cement has a free water content of 0%,porosity of 24%,permeability of 0.7×10-3μm2,low elasticity modulus,high Poisson’s ratio,and reasonable compressive strength,and is more elastic and flexible with capability to tolerate regional stresses.

Influence of Constituent Materials Properties on the Compressive Strength of in Situ Concrete in Kenya

The poor quality of Kenyan in situ concrete has necessitated research to establish the properties of the ingredient materials and their influence on the troubling rate of failure of reinforced concrete structures in the country during construction and usage. The compressive strength of concrete relies on the properties of the constituent materials, proportions of the mixture, workmanship, compaction method and curing conditions. This paper outlines findings of an experimental investigation on the properties of Kenyan concrete ingredient materials and their influence on the compressive strength of concrete in Kenya. Three types of cements (42.5N, 32.5R, 32.5N) from six different cement manufacturers and fine aggregates from three different regions in the country were used during the study. Cements and aggregates chemical analysis was done using the Atomic Absorption Spectrometer machine while the physical and the mechanical properties were checked based on the British Standards. The British DOE concrete mix design method was used to generate the concrete mix proportion and concrete was tested for early and ultimate compressive strengths at 7, 14 and 28 days. It was observed that the different cement brands have varying properties with CEM A having the highest ultimate compressive and flexural strengths. It was further noted that aggregates from the coastal region produced concrete of higher compressive strengths. When the commonly used mix design method was adopted, blended Portland cements produced concrete with ultimate compressive strengths lower than the designed target strengths. The study therefore recommends the development of a concrete mix design procedure for blended cement concrete production in Kenya.

Study of bond strength between various grade of Ordinary Portland Cement(OPC)and Portland Pozzolane Cement(PPC)mixes and different diameter of TMT bars by using pullout test

Since last two decades,the Portland Pozzolane Cement(PPC)is extensively used in structural concrete.But,till to date,a few literature is available on bond strength of concrete using PPC mixes.There are many literatures available on bond strength of concrete mixes using Ordinary Portland Cement(OPC).Hence,a comparative study was conducted on bond strength between OPC and PPC mixes.In the present investigation,total 24 samples consisting of M20,M35 and M50 grades of concrete and 16 and 25 mm diameter of TMT bar were tested for 7 and 28 days.The pullout bond test was conducted on each specimen as per IS:2770-1967/1997[1]and the results were observed at 0.25 mm slip at loaded end called as critical bond stress and at maximum bond load called as maximum bond stress.It was observed that the critical bond strength of PPC mixes is 10%higher than OPC mixes.Whereas,marginal improvement was noticed in maximum bond strength of PPC mixes.Hence,based on these findings,it could be concluded that development length for PPC mixes could be reduced by 10%as compared with same grade of OPC mixes.

Modeling of unconfined compressive strength of soil-RAP blend stabilized with Portland cement using multivariate adaptive regression spline

The recycled layer in full-depth reclamation (FDR) method is a mixture of coarse aggregates and reclaimed asphalt pavement (RAP) which is stabilized by a stabilizer agent. For design and quality control of the final product in FDR method, the unconfined compressive strength of stabilized material should be known. This paper aims to develop a mathematical model for predicting the unconfined compressive strength (UCS) of soil-RAP blend stabilized with Portland cement based on multivariate adaptive regression spline (MARS). To this end, two different aggregate materials were mixed with different percentages of RAP and then stabilized by different percentages of Portland cement. For training and testing of MARS model, total of 64 experimental UCS data were employed. Predictors or independent variables in the developed model are percentage of RAP, percentage of cement, optimum moisture content, percent passing of #200 sieve, and curing time. The results demonstrate that MARS has a great ability for prediction of the UCS in case of soil-RAP blend stabilized with Portland cement (R2 is more than 0.97). Sensitivity analysis of the proposed model showed that the cement, optimum moisture content, and percent passing of #200 sieve are the most influential parameters on the UCS of FDR layer.

Use of Plant-Based Accelerator to Enhance Rate of Gain of Strength of Kenyan Blended Cement

Concrete is the most widely used construction material in the world. The situation in the country is not an exception as most of the infrastructures in Kenya such as buildings, bridges, concrete drainage among others, are constructed using concrete. Sadly, the failure of buildings and other concrete structures is very common in Kenya. Blended Portland cement type 32.5 N/mm2 is the most widely used concrete binder material and is found in all parts of the country. Despite blended cement CEM 32.5 being the most commonly used cement type in construction industry in Kenya and most developing countries as a result of its low price and availability locally, its strength gain has been proven to be lower compared to when other types of cement are used due to quantity of pozzolanic material added to the blend. This paper outlines findings of an experimental investigation on the use of cypress tree extract as an accelerator to enhance rate of gain of strength on Kenyan blended cements. Six different blended cement brands locally available were used during the study. Cement chemical analysis was done using X-ray diffraction method while for the cypress extract, Atomic Absorption Spectrometer machine was used. Physical and mechanical properties were checked based on the British standards. The generation of the concrete mix design was done using the British DOE method and concrete was tested for the compressive strength at 7, 14, 21, 28, 56 and 90 days. It was observed that 15% dosage of the extract expressed as a mass percentage of the cement content gives the most improved compressive strength of concrete, 10.4% at 7 days and 9.5% at 28 days hence the optimum. It was further noted that when Cypress tree extract is used as an accelerator in the mix, the blended cement concrete achieves the design strength at 27 days saving 10 days of the project duration compared to when no accelerator is used while the ultimate strength is achieved at 67 days. The study therefore recommends the use of the cypress tree bark extract at a dosage of 15%, by mass, of the cement content as an accelerator when the structure is to be loaded at 28 days and waiting up to 39 days before loading the structure if no accelerator is used for blended cement concrete.

Properties of high calcium fly ash geopolymer pastes with Portland cement as an additive

The effect of Portland cement （OPC） addition on the properties of high calcium fly ash geopolymer pastes was investigated in the paper. OPC partially replaced fly ash （FA） at the dosages of 0, 5%, 10%, and 15% by mass of binder. Sodium silicate （Na2SiO3） and sodium hydroxide （NaOH） solutions were used as the liquid portion in the mixture： NaOH 10 mol/L, Na2SiO3/NaOH with a mass ratio of 2.0, and alkaline liquid/binder （L/B） with a mass ratio of 0.6. The curing at 60℃ for 24 h was used to accelerate the geopolymerization. The setting time of all fresh pastes, porosity, and compressive strength of the pastes at the stages of 1, 7, 28, and 90 d were tested. The elastic modulus and strain capacity of the pastes at the stage of 7 d were determined. It is revealed that the use of OPC as an additive to replace part of FA results-in the decreases in the setting time, porosity, and strain capacity of the paste specimens, while the compressive strength and elastic modulus seem to increase.

Analysis of Pore Structures and Their Relations with Strength of Hardened Cement Paste

Three cement samples were prepared, includi ng OPC consisted of 100wt% portland cement, PFA consisted of 70wt% portland cemen t and 30wt% fly-ash, and CA consisted of 70wt% portland cement and 30wt% modifi ed fly ash. The strength of hardened cement paste of these samples was tested an d their pore structures were determined by a mercury intrusion porosimeter. More over,the data of the pore structures of three samples were comprehensively analy zed. The relations between the pore structures and the compressive strength of t he three samples were studied. The experimental results show that the relations between the porosity determined by the mercury intrusion porosimeter and the com pressive strength are not notable, and the total pore surface area, the average pore diameter and the median pore diameter could be used to explain the differen ce of the strength of the tested samples.

Determination of the Pozzolanic Properties of Olotu Marine Clay and Its Potentials for Cement Production

The physical and chemical properties of marine clay at Olotu in Ilaje local government of Ondo State, Nigeria were investigated. Some of the physical properties investigated include plasticity index, linear shrinkage and firing characteristics (firing colour, shrinkage percentage, and water absorption capacity). The physical properties were determined using X-ray diffractometry method. The chemical composition was determined using Atomic Absorption Spectroscopy (AAS) method. All tests were carried out according to procedures specified by relevant British and American Standards. It was established that the physical and chemical properties were adequate to qualify it as pozzolanic material for cement production when compared with other pozzolanic materials and measured against relevant standards. The cement produced was tested for compressive strength and setting times and the results confirmed the appropriateness of the use of the clay as a pozzolana.

废弃泥浆制作水泥泡沫轻质土室内试验研究

为处理废弃泥浆,利用水泥协同泥浆制作泥浆水泥泡沫轻质土来修筑高速公路路基。制作了相同重度、不同水固比以及相同水固比、不同重度的泥浆水泥泡沫轻质土试块,测试在标准养护条件下28 d抗压强度,探究泥浆水泥泡沫轻质土水固比、水泥比例与重度对28 d抗压强度的影响。结果表明:泥浆泡沫轻质土的28 d抗压强度与水固比成负相关,与重度和水泥比例成正相关;配制合适的废弃泥浆水泥泡沫轻质土可用于高速公路路基修筑。此外,1 m3泡沫轻质土中,各掺量分别为水泥397 kg、干泥浆193 kg、水383.5 kg、发泡液27.1 kg时,流值为187.3 mm,试块28 d抗压强度可达2.62 MPa,且早期强度较高、水泥用量较少,可作为泥浆水泥泡沫轻质土的推荐配比。

疏水性侵蚀抑制剂对水泥水化影响及作用机理分析

疏水性侵蚀抑制剂使混凝土具有优异疏水效果,抑制了侵蚀性环境中介质传输,然而其作用机制尚未明确。本文对水泥浆体在不同疏水性侵蚀抑制剂(CAHA)掺量下的水化行为进行了研究,探究了其对水泥水化放热、水化物相、表面接触角、抗压强度等性能的影响。研究结果表明,CAHA降低了水泥浆体第一水化放热峰并延缓水泥水化,在水化前期抑制了钙矾石和氢氧化钙的生成,这种抑制作用在高掺量下更为显著。CAHA一定程度上降低了砂浆早期抗压强度,对28 d抗压强度影响并不明显。CAHA显著降低砂浆吸水率并使其具有疏水性。通过比对,推荐CAHA最佳掺量为胶凝材料质量的6%,此时水泥砂浆抗压强度损失较小且抗侵蚀性能明显提升。

外加剂对硫氧镁水泥泡沫混凝土性能影响

该文研究磷酸三钠、葡萄糖、有机酸C、有机酸盐D四种外加剂复掺对硫氧镁水泥泡沫混凝土抗压强度和耐水性的影响。并采用XRD、SEM表征硫氧镁水泥泡沫混凝土试样的物相组成和微观结构。结果表明,适当掺量的四种外加剂都能提高硫氧镁水泥泡沫混凝土抗压强度及耐水性,有机酸C对硫氧镁水泥泡沫混凝土抗压强度影响较大,有机酸C掺量为0.6%时,试块28 d抗压强度达到1.91 MPa;磷酸三钠可以有效改善硫氧镁水泥泡沫混凝土耐水性,当磷酸三钠掺量0.6%时,试块软化系数达0.8;复掺外加剂试样强度与耐水性得到提升,其28 d抗压强度达到2.1 MPa,是不掺外加剂试样的1.58倍,其软化系数达0.92。

硅酸盐水泥基固化剂流态固化土抗压强度研究

针对实际工程对渣土处理和涵背、涵顶回填的需求,采用硅酸盐水泥分别和矿粉、粉煤灰复合作为固化剂,研究不同固化剂、不同固化剂掺量、不同水固比等条件下流态固化土强度发展规律。结果表明:流态固化土抗压强度随着试验龄期的延长而增长,相同掺量下,采用矿粉作为掺合料的流态固化土抗压强度要明显高于粉煤灰;随着掺量的增加,粉煤灰流态固化土抗压强度显著降低,28 d强度降低了13.6%,而矿粉流态固化土抗压强度具有一定程度的提高,28 d强度提高了12.6%。随着固化剂掺量增加,流态固化土抗压强度提高。随着水固比的增大,抗压强度均呈现一定程度的降低趋势。

Factors Influencing Strength of Super Absorbent Polymer(SAP)Concrete

Super absorbent polymers (SAPs) are gradually being applied in concrete production as internal curing agents. SAP can effectively reduce early age autogenous shrinkage of concrete, alleviate the hazards caused by concrete cracking and improve its freeze–thaw resistance. However, the relationships between SAP dosage, SAP particle size and the water–cement ratio of concrete have certain influences on the evolution of the compressive strength of SAP-incorporated concrete. In this study, experiments were conducted to investigate the relationships between the water–cement ratio of concrete, the SAP dosage and SAP particle size. The significant factors influencing concrete strength are determined and equations are proposed for predicting the strength of SAP-incorporated concrete at 3, 7 and 28 days. The findings from this study, such as the SAP dosage should not be larger than 0.2%, are expected to form a theoretical basis for the rational use of SAP as an additive to concrete. © 2017, Tianjin University and Springer-Verlag Berlin Heidelberg.

初凝超30 min超早强UHPC制备及其机理

针对既有交通线路快速抢通和抢通后寿命确保的需要,研发了具有足够施工时间的超早强(数小时达到开放强度)超高性能混凝土(UHPC)。基于最大密实度理论的UHPC配方,试验研究了普通硅酸盐水泥(OPC)替代率对硫铝酸盐-硅酸盐复合体系(SAC-OPC体系)混凝土力学性能与施工性能的影响,确定了OPC替代率;通过正交试验确定影响SAC-OPC体系混凝土力学性能和工作性能的早强组分(硫酸锂、硫酸铝)、增强组分(纳米碳酸钙)、调凝组分(粉体缓凝剂、四硼酸钠),制备了初凝时间36 min、3 h抗压/抗折强度41.4/17.0 MPa的超早强UHPC,以及初凝时间40 min、3 h抗压/抗折强度36.2/13.9 MPa的超早强UHPC。通过SEM和XRD分析,探究了具有足够施工时间超早强UHPC的性能形成机理。结果表明:随OPC替代率增大,UHPC的凝结时间先减后增,扩展度持续增大,早期力学性能大致呈下降趋势,后期力学性能大致呈上升趋势;超早强与初凝时间延长主要源于协同水化作用与早强组分、增强组分和调凝组分的累加效应。

两种羟基羧酸盐类缓凝组分对水泥物理性能的影响

目的为了延缓混凝土初凝和终凝时间而不影响混凝土后期强度,对两种羟基羧酸盐类缓凝组分进行分析研究。方法分析两种缓凝组分在不同掺量下对普通硅酸盐水泥的凝结时间、扩展度、强度及水化热的影响规律,利用扫描电子显微镜观察水泥的微观结构特征。结果掺入缓凝组分后,水泥的凝结时间延长了,掺量为0.07%时物理性能最佳,此时初凝时间分别延长了299 min和218 min,扩展度分别延长了35 mm和30 mm,56 d抗折强度分别增加了12.22%和9.65%,56 d抗压强度分别增加了15.67%和11.39%;从微观结构的特征可以看出随缓凝组分掺量增加,水化速率减慢,各水化产物之间交叉连生,形成更为密实的网状结构,改善了水泥试样的后期强度。结论液体缓凝组分相较于固体缓凝组分能更好地起到缓凝作用,延缓了水泥水化反应及水化产物的生成时间,进而改善了生成物之间的搭接结构,提高了水泥后期强度。

水下不分散灌浆料的制备及性能研究

以普通硅酸盐水泥为主要胶凝材料制备了一种水下不分散灌浆料,选取硅酸盐水泥、硫铝酸盐水泥和无水石膏的三元胶凝体系,采用单因素试验法,研究了水料比、高分子絮凝剂掺量、聚羧酸减水剂粉末掺量这3个关键因素对水下不分散灌浆料流动度、抗分散性、抗压强度的影响,确定出了最佳掺量。结果表明:当水料比为0.14、高分子絮凝剂掺量为0.15%、聚羧酸减水剂粉末掺量为0.55%时,水下不分散灌浆料的初始流动度为258 mm,30 min流动度为256 mm;7 d、28 d水下抗压强度分别为35.76 MPa、53.09 MPa;水下抗分散性为Ⅰ,水下不分散灌浆料的水下抗分散性好,可用于C40混凝土修补加固。

改性组分对掺加无碱液体速凝剂水泥早期性能的影响

目的 研究掺入基于多元醇与铝盐的改性组分改善掺加无碱液体速凝剂后的水泥早期强度等性能。方法 控制速凝剂质量比不变,测试不同改性组分质量比的普通硅酸盐水泥的凝结时间和抗压强度,通过28 d、90 d抗压强度比验证强度变化规律,分析水化放热特点,利用X射线衍射仪、扫描电子显微镜探究并分析试样微观表征。结果 掺入改性组分后,水泥的凝结时间缩短,1 d的抗压强度提高,水化放热速率增大,并伴有大量针状钙矾石生成,当掺量为0.04%时效果最佳,此时的初凝时间为1.72 min,终凝时间为2.37 min, 1 d抗压强度达到了10.01 MPa。结论 改性组分有利于无碱液体速凝剂加快水泥水化放热速率,促进试样中针状钙矾石生成,有利于网络空间结构的搭建,很好地改善了水泥水化性能,提高了早期抗压强度。

泡沫掺量对超轻质硫氧镁基泡沫混凝土性能的影响

硫氧镁水泥具有轻质、导热系数低、耐火等优点,将其制备成泡沫混凝土并应用于建筑外墙保温系统具有巨大的市场潜力。本文通过加入高稳定改性泡沫来调控超轻质硫氧镁基泡沫混凝土的密度,并结合扫描电子显微镜(SEM)、光学显微镜(OM)等测试研究了气孔结构的变化,探究了密度和孔结构变化对超轻质硫氧镁基泡沫混凝土抗压强度和导热系数的影响。结果表明:随着高稳定改性泡沫掺量的增加,超轻质硫氧镁基泡沫混凝土的气孔数量增多且平均孔径明显减小,密度逐渐减小,抗压强度逐渐降低;当泡沫掺量为250%(质量分数)时,超轻质硫氧镁基泡沫混凝土的密度降低至88.33 kg/m^(3),导热系数降低至0.0382 W/(m·K)。