Relationships between mechanical properties of cement stabilized materials

A laboratory testing programme of granular materials stabilized with cement has been implemented in order to determine the influence of changes in mix composition on their mechanical characteristics. The elements of the composition of stabilized mixes such as gradation, cement content, cement type, density and curing time were varied. The results obtained were analysed statistically and three types of correlation were determined. It is concluded that the relationship between the dynamic modulus of elasticity and the pulse velocity is almost unaffected by individual composition parameters, while the relationship between compressive and tensile strength, and especially that of compressive strength and dynamic modulus of elasticity, is dependent on these parameters.     

Properties of hardened concrete containing treated expanded polystyrene beads

This paper reports the results of an experimental investigation into the properties of hardened concrete containing chemically treated expanded polystyrene beads. The results showed that the strength, stiffness and chemical resistance of polystyrene aggregate concrete of a constant density were affected by the water to cement ratio. Drying shrinkage after 84 days of drying for polystyrene concretes, having 10 mm coarse aggregate and a nominal density of 1300 kg/m³, were 730 and 655 microstrains. Empirical equations were developed to relate the strength and pulse velocity and to predict the modulus of elasticity from its strength.     

Strength properties of steel slag stabilized mixes

A new type of low-strength concrete made with steel slag and gravel was investigated in this report. Increasing the amount of cement or steel slag in the mix increased the maximum dry density and optimum moisture content of the concrete. Additionally, the compressive and indirect tensile strength of the concrete increased with curing age. The strength of mixes with low cement contents increased with the slag content, while that of mixes with higher cement contents decreased with slag content. Finally, the average indirect tensile strength for all mixes as a percentage of compressive strength was ∼14%.     

Comparison of Dynamic Young’s Modulus of Thin Concrete Disks to Stress Wave–Based Nondestructive Evaluation Findings

Stress wave–based nondestructive evaluation (NDE) techniques are frequently used for in-situ evaluation of concrete. Stress wave velocity in a material is related to Young’s modulus of elasticity. Cores for in-situ compressive strength are subject to a minimum length-to-diameter ratio requirement that enforce large specimen sizes. Thin circular disks sawn from cylinders or cores are widely used in measurement of chloride or air permeability of concrete. While these methods provide useful information on concrete properties with depth, the capability of measuring changes in mechanical properties such as elastic Young’s modulus in small depth increments is of value to both researchers and consulting engineers conducting condition assessment or NDE, particularly when damage gradients exist. Changes in properties over relatively small depths may be undetected otherwise due to limitations of test method, equipment, or imposed specimen size. This study presents applications of Young’s modulus of thin concrete disks to structural assessment projects involving damage and damage gradients. In-situ nondestructive ultrasonic pulse velocity (UPV) testing was used in identification of affected areas. Young’s modulus of thin concrete disks was used in interpretation of the NDE results and provided an improved understanding of the extent of damage that was indicated using NDE. Two different case studies are discussed: exposure to fire and exposure to thermal shock and cryogenic temperatures. The use of thin disks enabled determination of mechanical properties of relatively thin layers of concrete and, therefore, provided a means to quantitatively assess the extent of damage gradients. Confirmation of NDE results using modulus data and analytical modeling using the relationship between Young’s modulus and pulse velocity provided improved understanding of NDE findings reducing uncertainty in engineering analysis and improving repair recommendations.     

混杂纤维增强再生砖骨料混凝土增强机制与抗压性能计算方法

通过钢-聚烯烃混杂纤维增强再生砖骨料混凝土（HF/RBAC）的抗压与弹性模量试验,研究了再生砖骨料（RBA）取代率、混杂纤维掺量、纤维种类对混凝土抗压强度和弹性模量的影响。根据RBA的XRD图谱、X-CT图像、RBA火山灰活性成分与水泥水化产物反应原理及能量平衡原理,分析了HF/RBAC的破坏机制和纤维增强机制。研究表明,当RBA全取代天然骨料（NA）时,HF/RBAC立方体抗压强度、轴心抗压强度和弹性模量分别降低了36.72%、24.95%和43.53%。当钢-聚烯烃混杂纤维体积掺量为1.5%时,HF/RBAC立方体抗压强度、轴心抗压强度和弹性模量分别增加了20.51%、30.33%和35.84%。最后,提出了考虑RBA压碎指标和取代率、纤维种类和掺量等因素影响的HF/RBAC抗压强度和弹性模量的计算方法。     

Accelerated carbonation and performance of concrete made with steel slag as binding materials and aggregates

Steel slag has been used as supplementary cementitious materials or aggregates in concrete. However, the substitution levels of steel slag for Portland cement or natural aggregates were limited due to its low hydraulic property or latent volume instability. In this study, 60% of steel slag powders containing high free-CaO content, 20% of Portland cement and up to 20% of reactive magnesia and lime were mixed to prepare the binding blends. The binding blends were then used to cast concrete, in which up to 100% of natural aggregates (limestone and river sands) were replaced with steel slag aggregates. The concrete was exposed to carbonation curing with a concentration of 99.9% CO₂ and a pressure of 0.10 MPa for different durations (1d, 3d, and 14d). The carbonation front, carbonate products, compressive strength, microstructure, and volume stability of the concrete were investigated. Results show that the compressive strength of the steel slag concrete after CO₂ curing was significantly increased. The compressive strengths of concrete subjected to CO₂ curing for 14d were up to five-fold greater than that of the corresponding concrete under conventional moist curing for 28d. This is attributed to the formation of calcium carbonates, leading to a microstructure densification of the concrete. Replacement of limestone and sand aggregates with steel slag aggregates also increased the compressive strengths of the concrete subjected to CO₂ curing. In addition, the concrete pre-exposed to CO₂ curing produced less expansion than the concrete pre-exposed to moist curing during the subsequent accelerated curing in 60 °C water. This study provides a potential approach to prepare concrete with low-carbon emissions via the accelerated carbonation of steel slag.     

Effect of ground granulate blast-furnace slag on corrosion performance of steel embedded in concrete

Corrosion of steel in concrete is one of the major causes of premature deterioration of reinforced concrete structures, leading to structural failure. To prevent the failure of concrete structures because of corrosion, impermeable and high performance concretes should be produced various mineral admixtures. In this study, plain and reinforced concrete members are produced with mineral admixtures replacing cement. Ground granulated blast-furnace slag (GGBFS) has replaced cement as mineral admixture at the ratios of 0%, 25% and 50%. The related tests have been conducted at the ages of 28 and 90, after exposing these produced plain and reinforced concrete members to two different curing conditions. The unit weight, ultrasonic pulse velocity, splitting tensile and compressive strength tests are conducted on plain concrete members. Half-cell potential and accelerated corrosion tests are also conducted on reinforced concrete members. According to the test results, it is concluded that the curing age and type are important and corrosion resistant concrete can be produced by using GGBFS mineral admixture at the ratio of 25%.     

Properties of interfacial transition zones (ITZs) in concrete containing recycled mixed aggregate

Concretes containing mixed recycled aggregate (RA) have a larger number of coarse aggregate/paste interfacial transition zones (ITZs) than conventional concretes, due to the various component materials present in recycled aggregate. This study investigated the properties of various RA/paste ITZs in concrete using nanoindentation and scanning electron microscopy (SEM) and analysed the possible impact of the properties of the ITZs on the macro-mechanical performance of recycled concrete. It was found that the elastic modulus of the ITZ varies with the type of constituent materials present in recycled aggregate, with ITZs associated with organic components (e.g. wood, plastic and asphalt) exhibiting lower minimum elastic modulus values. The impact of ITZ properties on macro-mechanical properties of concrete depends on the relative content of different constituent materials present in the recycled aggregate and the micro-mechanical properties of the ITZs involved.     

竹塑模压异型板包装材料工艺

目的 传统塑料包装透气性较差,不利于环保,为解决这些缺陷,研发一种塑料-细竹丝模压异型板件的新型外固定用包装材料,并通过实验方法确定其性能.方法 首先,介绍塑料-细竹丝模压异型板件新型包装材料的特点与成型工艺;其次,通过实验对塑料-细竹丝模压异型板件包装材料制造时最佳竹塑比进行确定;最后,利用概率设计理论求解出异型板件包装材料主方向的弹性模量,并通过实验对其理论公式进行验证.结果 当竹塑比值为0.150时,异型板件包装材料的各项性能较好,上异型板件包装材料单位质量的最大抗压力平均值达到4.33 kN/kg,下异型板件包装材料单位质量的最大抗压力平均值达到5.26 kN/kg.力学实验结果显示,所建立异型板件包装材料的弹性模量理论求解公式正确,且细竹丝的加入提高了原有包装材料的力学性能.结论 新型包装材料具有较好的稳定性和透气性,更加环保,是传统塑料包装材料的理想换代产品.文中研究将推进我国异型板件包装材料工业化的发展,并为异型板件包装材料产业化加工设备的设计制造提供理论和实验依据.     

橡胶对水泥基材料干燥收缩性能的影响

为了考察橡胶增加水泥基材料干燥收缩量的机制,以橡胶水泥砂浆作为研究对象,采用毛细管张力理论分析了造成水泥砂浆干燥收缩的因素。使用压汞试验研究橡胶/水泥砂浆的孔结构,并进行了弹性模量和干燥收缩试验。研究结果表明,橡胶掺入会降低水泥砂浆的弹性模量,增加其孔隙率和干燥收缩量,且相同掺量条件下,小粒径橡胶的作用效果更明显。基于试验数据,考虑橡胶掺入对砂浆弹性模量的折减系数KE和橡胶掺入对毛细孔(孔径50nm的孔隙)数量的增加系数K_h,拟合了橡胶对水泥砂浆干燥收缩的影响参数δ_(mr)。     

Mechanical properties of cement-treated aggregate material – A review

Cement-treated aggregate material (CTAM) is a traditional material applied in road bases and sub-bases. Its mixture proportioning design method applied in the last decades is tentative, time-consuming and cost-effective. There is no advanced technique to design the mixture proportioning of CTAM so far. Therefore, the problem of designing a CTAM mixture is the lack of an effective procedure that allows predicting its mechanical properties from mixture parameters like the mix composition and the characteristics of components. For cement concrete and asphalt concrete such prediction techniques already exist.This paper herein reviews the influence of mixture variables on the mechanical properties of CTAM. These properties include the unconfined compressive strength (UCS), the tensile strength and the elastic modulus. It was found that the UCS is normally taken as an important quality indicator of CTAM. Variables influencing the UCS, such as cement content, curing time, degree of compaction and so on, play different roles to determine the performance of CTAM. Models to predict the tensile strength and the elastic modulus are always correlated to the UCS. Evidence may be given that prediction models for the mechanical properties of CTAM may be established on basis of mixture parameters.     

循环流化床固硫灰渣低收缩水泥的制备及性能

通过分别使用循环流化床(CFBC)固硫灰、渣代替部分原材料制备低收缩水泥熟料,加入质量分数为10%的石膏即得到CFBC固硫灰、渣低收缩水泥,然后利用X射线衍射、扫描电镜等方法研究水与水泥的质量比(简称水灰比)对CFBC固硫灰渣低收缩水泥水化程度、抗压强度和线性膨胀率的影响。结果表明,随着水灰比的增加,CFBC固硫灰渣低收缩水泥的主要水化产物钙矾石数量增多,未水化的硅酸二钙含量减少,水化程度增大;而该水泥线性膨胀率与水灰比呈正比关系,抗压强度与其呈反比关系;利用固硫灰制备的水泥早期膨胀率随着水化时间而增大,但后期由于石膏量的不足,膨胀率则随着水化时间而减小。     

Effect of curing time on granulated blast-furnace slag cement mortars carbonation

Currently, ground granulated blast-furnace slag cements use in cement-based materials is being increasing because perform well in marine and other aggressive environments. However, mortars and concretes made of this type of cement exhibit high carbonation rates, particularly in badly cured cement-based materials and when high blast-furnace slag contents are used. Concrete reinforcement remains passive but can be corroded if the pore solution pH drops as a result of the carbonation process promoting the reinforced concrete structure failure during its service life. Results show the very sensitive response to wet-curing time of slag mortars with regard to the natural carbonation resistance. Then, a minimum period of 3–7 days of wet curing is required in order to guarantee the usual projected service life in reinforced concrete structures. In this work, estimation models of carbonation depth and carbon dioxide diffusion coefficient in ground granulated blast-furnace slag mortars as a function of the curing period and the amount of ground granulated blast-furnace slag are proposed. This information will be useful to material and civil engineers in designing cement-based materials and planning the required curing time depending on their ground granulated blast-furnace slag content.     

Influence of elevated temperatures on the mechanical properties of blended cement concretes prepared with limestone and siliceous aggregates

The investigation performed was aimed at showing the influence of high temperatures on the mechanical properties and properties that affect the measurement by non-destructive methods (rebound hammer and pulse velocity) of concrete containing various levels (10% and 30%) of pozzolanic materials. Three types of Pozzolans, one natural pozzolan and two lignite fly ashes (one of low and the other of high lime content) were used for cement replacement. Two series of mixtures were prepared using limestone and siliceous aggregates. The W/b and the cementitius material content were maintained constant for all the mixtures. Concrete specimens were tested at 100, 300, 600 and 750 °C for 2 h without any imposed load, and under the same heating regime. At the age of 3 years, tests of compressive strength, modulus of elasticity, rebound hummer and pulse velocity were come out. Results indicate that the residual properties of concrete strongly depend on the aggregates' and the binder type. Relationships between strength of concrete as well as rebound and pulse velocity versus heating temperatures are established. The above results are evaluated to establish a direct relationship between non-destructive measurements and compressive strength of concrete exposed to fire.     

掺矿渣活性粉末混凝土配制技术的研究

活性粉末混凝土(RPC)是一种超高性能的水泥基材料.本文在传统RPC配制技术的基础上,掺入矿渣组分,配制出新型的混凝土材料,并对该混凝土的力学性能、配合比以及养护条件等进行系统的研究.实验显示,该种混凝土具有较高的力学性能;存在一个最优配合比;热养护有助于改善RPC的微观结构,提高其力学性能.材料的微观结构致密,其CH的含量因二次火山灰反应已经很低.     

碳酸化钢渣和矿渣作硅酸盐水泥混合材水化性能研究

通过对钢渣碳酸化前后的硅酸盐相提取及水化放热性能和将碳酸化钢渣和矿渣作为混合材的硅酸盐水泥的胶砂强度和水化产物种类的测定,以及对它们微观形貌的观察,研究了碳酸化钢渣对胶凝体系水化性能的影响.结果表明,碳酸化使钢渣中硅酸盐相的含量由47.06％下降至14.38％;碳酸化促进了钢渣的早期水化,抑制其后期水化;在配比相同的条件下,碳酸化钢渣-矿渣-硅酸盐熟料体系试样的3、28d抗压强度较未碳酸化钢渣-矿渣-硅酸盐熟料体系试样的高;碳酸化生成的CaCO3促进了熟料的水化;碳酸化钢渣促进了胶凝体系中AFt的生成,且生成水合碳铝酸钙.     

Investigation on the application of steel slag-fly ash-phosphogypsum solidified material as road base material

The aim of the present work is to prepare a new type of steel slag-fly ash-phosphogypsum solidified material totally composed with solid wastes to be utilized as road base material. The mix formula of this material was optimized, the solidified material with optimal mix formula (fly ash/steel slag=1:1, phosphogypsum dosage=2.5%) results in highest strength. The strength development, resilience modulus and splitting strength of this material were studied comparing with some typical road base materials, the 28- and 360-day strength of this material can reach 8MPa and 12MPa, respectively, its resilience modulus reaches 1987MPa and splitting strength reaches 0.82MPa, it has higher early strength than lime-fly ash and lime-soil road base material, its long-term strength is much higher than cement stabilized granular materials, the solidified material has best water stability among those road base materials, it can be engineered as road base material with competitive properties. The strength formation mechanism of this solidified material is discussed also.     

Factors contributing to early age shrinkage cracking of slag concretes subjected to 7-days moist curing

The objective of this study was to investigate all the factors contributing to early age shrinkage cracking in concrete, namely, shrinkage, tensile creep, tensile elastic modulus, tensile strength of concretes, and to study the effect of slag as a binder on these factors. The above-mentioned factors were measured in early age concretes made with 0, 35, 50 and 65% level replacement of ordinary Portland cement by slag. All the concretes studied were moist cured for 7-days. It was found that, at lower slag replacement levels (0, 35 and 50%), the tensile strength decreased with increasing slag replacement. However, this is more than compensated by decreasing tensile elastic modulus and shrinkage. There was no significant change found in tensile creep with the changing slag levels. The study shows that the influence of the tensile elastic modulus is a major consideration for early age cracking of slag concretes.     

Effect of hot-dry curing environment on the intrinsic properties of repair materials

The paper examines the properties of five different types of repair materials, including conventional cementitious, polymer and polymer-modified repair mortars. Assessment was carried out on the basis of the engineering properties (compressive strength, tensile strength and modulus of elasticity), pore structure (porosity and pore size distribution), transport properties (permeability and diffusion) and shrinkage. These properties were measured up to the age of 28 days after curing in a hot-dry environment.

The epoxy resin repair mortar showed superior strength and transport characteristics with a very fine pore structure; however, its modulus of elasticity was remarkably low when compared with that of normal- and high-strength concretes. A hot-dry curing environment adversely affects the shrinkage and performance-related properties of conventional repair mortars; however, small improvements could be achieved by the use of mineral admixtures (fly ash and silica fume). The paper discusses also the different testing techniques which could be used to assess the potential performance of concrete repair mortars.     

基于超声波测试的片岩单轴抗压强度预测模型

岩石单轴抗压强度是岩土工程中最基础、最重要的参数之一,建立其快速、方便、经济的预测方法一直是岩土界的研究热点。为了获取片岩单轴抗压强度的预测模型,基于超声波试验和单轴压缩试验数据,对福建某矿山的片岩岩样分别开展了单轴抗压强度与纵波波速、横波波速、纵波模量、横波模量、动弹性模量和静弹性模量的回归性分析,并各自建立了线性、对数、多项式、指数函数和幂函数5种回归模型。分析表明,除了动弹性模量以外,其他参量都易受空间变异性和各向异性影响,不适合用于片岩单轴抗压强度的预测。最终,通过拟合度、所包含参量、量纲平衡、测试方法以及显著性分析,确定基于动弹性模量建立的线性回归模型是最合理、可靠、方便的片岩单轴抗压强度预测模型。研究成果可为开展岩石单轴抗压强度预测的相关理论研究和工程应用提供参考和帮助。