Effect of quartz-powder on the properties of conventional cementitious materials and geopolymers

In the recent years, grinding technology has been brought a new product with prospective properties. If quartz sand is ground, a new product is obtained with superior properties than its original. The literature contains some studies focused on employing quartz powder (QP) in traditional cementitious materials and geopolymers as additives to obtain modified matrices. This article presents a brief of the past studies fixated on adding QP into different matrices. Fresh and hardened properties have been briefed.

This review was submitted as part of the 2018 Materials Literature Review Prize of the Institute of Materials, Minerals and Mining run by the Editorial Board of MST. Sponsorship of the prize by TWI Ltd is gratefully acknowledged.     

Effect of shrinkage reducing admixture on flexural behaviors of fiber reinforced cementitious composites

The use of shrinkage reducing admixture (SRA) at various concentrations was investigated in fiber reinforced cementitious composites. Both mortar and high strength concrete (HSC) matrices were tested. Two types of fibers—steel and polypropylene—were assessed. The effect of SRA was measured on the fundamental properties such as surface tension of the bulk fluids and the contact angle developed between the fibers and the bulk fluids, on the fresh properties such as the air content and the density, and finally on the hardened mechanical properties, specially the flexural behaviors. It was noted that SRA enhances the wettability of fibers and reduces the air content of fiber reinforced cement mortars, while critical SRA concentrations are existing. SRA with critical concentration can significantly improve the flexural toughness and residual strength of steel fiber reinforced cement mortar. In the case of polypropylene fiber, SRA is not as effective in enhancing the flexural behaviors as it is in the case of steel fiber. SRA is generally ineffective in reducing the air content of HSC and the properties of steel fiber reinforced HSC with SRA are inferior to those without SRA.     

Properties of high performance concrete containing fine-ground ceramics as supplementary cementitious material

This paper presents experimental work regarding the basic physical characteristics, mechanical and fracture-mechanics properties, durability characteristics, hydric and thermal properties of high performance concrete (HPC) with up to 60% of Portland cement replaced by fine-ground ceramics. Experimental results show that the amount of the ceramics in the mix is limited mainly by the resistance against de-icing salts which is found satisfactory only up to the cement replacement level of 10%. The mechanical and water transport properties are not significantly impaired by ceramic additions of up to 20%, whereas the effective fracture toughness, specific fracture energy, and chemical resistance (to MgCl₂, NH₄Cl, Na₂SO₄, HCl) are effectively maintained up to 40%. The frost resistance, water vapor transport and storage parameters and thermal properties are not significantly impaired even up to a 60% replacement level.     

The influence of temperature on autogenous volume changes in cementitious materials containing shrinkage reducing admixtures

This research examines the influence of temperature on unrestrained and restrained autogenous volume changes in cementitious systems containing shrinkage reducing admixtures (SRAs). The apparent activation energy of cement hydration is determined using measurements of isothermal conduction calorimetry. Time-temperature (equivalent-age based) transformations are applied to extract the apparent activation energy of cement hydration (reactions). The results indicate that while equivalent-age transformations are a suitable procedure for describing the influence of temperature on chemical reactions, they are an inappropriate approach to describe the evolution of volume changes in cementitious materials cured at different temperatures. It is noted that while SRAs do not substantially alter the temperature sensitivity of hydration reactions, their ability to induce early-age expansions negates the use of maturity (equivalent age) approaches in describing autogenous deformations in these materials. Efforts are made to better describe the thermodynamic-limitations of autogenous RH change (self-desiccation) and the need to account for viscoelastic (i.e., creep) and damage (i.e., microcracking) considerations in interpreting the residual stress development response of cement-based materials cured at different temperatures.     

Effect of granulometry on cementitious properties of ladle furnace slag

Ladle furnace slag (LFS), a by-product of the steel making process, was tested for its potential use as a supplementary cementing material. The material used for the tests was screened or ground, producing three samples of different fineness, and the granulometry of these LFS samples was also tested by particle size analysis. Their chemical and mineralogical composition was assessed by chemical analysis, X-ray diffraction and thermogravimetric analysis. Finally, in order to determine the cementitious and pozzolanic character of LFS in relation to its granulometry, slag-lime and slag-cement mortars were produced and tested in compression. The results show that although LFS is a weak supplementary cementing material, it shows some self-cementing and pozzolanic properties that can be enhanced by screening or grinding the raw material. Even though different levels of fineness and granulometry can be reached with each method, generally, grinding seems to improve LFS binding properties more than sieving.     

Biomass fly ash effect on fresh and hardened state properties of cement based materials

Cement pastes and mortars were prepared by replacing ordinary Portland cement with different dosages of biomass fly ashes (0, 10, 20 and 30% BFA) whilst in dry condition. The effect of BFA on the flow behaviour (spread on table and rheology), setting time, temperature of hydration and electrical resistivity was studied in this experimental research. Increasing the amount of BFA in the compositions required extra dosage of water, as a result of particles fineness, tendency for agglomeration and retention/absorption of water molecules. As a consequence, the relative amount of free water diminishes and the flowability is poorer. The introduction of BFA also led to an increase in setting time, while the resistivity obtained from the impedance measurements tends to be lower than the reference paste (ash-free). The higher concentration of mobile species in the pore solution, namely sodium ions introduced by the ash, explains that tendency. The hydration temperature of cement pastes tends to decrease with the level of cement to ash replacement. Between the two tested ashes (from grate and fluidized sand bed furnaces), differences in particle size and shape, in the amount of residual organic matter and concentration of inorganic components define minor changes in the workability and setting behaviour. Therefore, the introduction of biomass fly ashes affects the hardened state features but do not compromise them.     

Thixotropy and structural breakdown properties of self consolidating concrete containing various supplementary cementitious materials

In this study, thixotropy and structural breakdown of 57 self-consolidating concrete (SCC) mixtures containing various supplementary cementitious materials (SCM) were investigated by different approaches. The effects of SCM type and content on high range water reducer demand and plastic viscosity were also studied. For these purposes, various amounts of silica fume (SF), metakaolin (MK), Class F fly ash (FAF), Class C fly ash (FAC) and granulated blast-furnace slag (BFS) were utilized in binary, ternary, and quaternary cementitious blends in three water/binder (w/b) ratios. Results showed that except BFS, use of SCM in SCC mixtures increased thixotropy values in comparison with the mixtures containing only portland cement (PC). Good correlations were established between structural breakdown area and drop in apparent viscosity values for all w/b ratios. The different methods used to evaluate the thixotropy and structural breakdown got more consistent with each other as w/b decreased.     

纳滤膜材质对高含盐体系中有机物截留性能的影响研究

为获得纳滤膜材质对高含盐体系中有机物截留性能的影响规律,采用截留分子量相近的有机纳滤膜和陶瓷纳滤膜对模拟高含盐体系中有机物的截留性能进行研究比较,考察运行时间、盐浓度、跨膜压差、有机物浓度等因素对截留效果的影响.结果表明,两种纳滤膜运行30 min后截留性能即可稳定;随着盐浓度的增加,膜的渗透通量和膜对有机物的截留率都下降,其中陶瓷纳滤膜对有机物的截留效果优于有机纳滤膜;有机物浓度和跨膜压差对两种膜的截留性能影响较小.因此,在高含盐体系中,截留分子量相近的陶瓷纳滤膜相比于有机纳滤膜,前者具有更大的通量和更高的有机物截留率.     

氨基磺酸盐高效减水剂的研发及复配

采用缩合聚合反应合成了低塌落度损失的氨基磺酸盐高效减水剂。探讨了缩合法生产氨基磺酸盐高效减水剂的工艺过程以及复配对高效减水剂性能的影响。     

Microstructure variability and macroscopic composite properties of high performance fiber reinforced cementitious composites

High performance fiber reinforced cementitious composites have made major advances in recent years, to the point where they are being adopted in building and bridge constructions. The most significant advantage of HPFRCC over conventional concrete is their high tensile ductility. However, the tensile strain capacity has been observed to vary, most likely as a result of the variability of the microstructure derived from the processing of these materials.This paper describes the composite property variability, as well as the variability of the material microstructure. Scale linkage is discussed. In particular, the tensile stress–strain curves, and the crack pattern on uniaxially loaded specimens are presented. The treatment of random fibers in micromechanical models, and tailoring of matrix flaw size distribution for saturated multiple cracking are examined. It is suggested that robust composite properties can be achieved by deliberate control of microstructure variability. Some open issues concerning the randomness of microstructures and possibly related macroscopic behavior are also identified. Further gains in composite property control may be expected from improvements in characterization and modeling of the microstructure randomness.     

Engineering properties of concrete containing natural zeolite as supplementary cementitious material: Strength,toughness, durability,and hygrothermal performance

A complex analysis of engineering properties of concrete containing natural zeolite as supplementary cementitious material in the blended Portland-cement based binder in an amount of up to 60% by mass is presented. The studied parameters include basic physical characteristics, mechanical and fracture–mechanics properties, durability characteristics, and hygric and thermal properties. Experimental results show that 20% zeolite content in the blended binder is the most suitable option. For this cement replacement level the compressive strength, bending strength, effective fracture toughness, effective toughness, and specific fracture energy are only slightly worse than for the reference Portland-cement concrete. The frost resistance, de-icing salt resistance, and chemical resistance to MgCl₂, NH₄Cl, Na₂SO₄, and HCl are improved. The hygrothermal performance of hardened mixes containing 20% natural zeolite, as assessed using the measured values of water absorption coefficient, water vapor diffusion coefficient, water vapor sorption isotherms, thermal conductivity, and specific heat capacity, is satisfactory.     

Specimen size effect on the residual properties of engineered cementitious composites subjected to high temperatures

In this study, size effect on the residual properties of Engineered Cementitious Composites (ECC) was investigated on the specimens exposed to high temperatures up to 800 °C. Cylindrical specimens having different sizes were produced with a standard ECC mixture. Changes in pore structure, residual compressive strength and stress–strain curves due to high temperatures were determined after air cooling. Experimental results indicate that despite the increase of specimen size, no explosive spalling occurred in any of the specimens during the high temperature exposure. Increasing the specimen size and exposure temperature decreased the compressive strength and stiffness. Percent reduction in compressive strength and stiffness due to high temperature was similar for all specimen sizes.     

高温石墨炉用碳素材料的热辐射性能研究

以碳素材料微观结构与表面形貌为基础,研究了不同型号的碳/碳复合材料及石墨材料的光谱发射率。研究表明,石墨微晶结构规整度与表面微观形貌是影响碳素材料光谱发射率差异的因素。为评价碳素热辐射性能、设计高效热场提供理论指导。     

Effect of water soluble polymers on the early age shrinkage of cementitious composites by using the ring test method

The effect of water soluble polymers (WSP) on the shrinkage deformation at an early age is reported in this paper. Commercially available hydroxy propyl methyl cellulose (HPMC) with two different molecular weights was employed in the cementitious composites with various mixing ratios. A restrained shrinkage test was conducted with a steel ring in accordance with ASTM C1581-04. In addition to the steel ring's strain, the surface tension, viscosity, internal relative humidity (RH) and crack propagation were also investigated. The polymer-modified cementitious composites were found to be effective in reducing the crack tendency by extending the age at cracking in comparison to the control mixture. The test results also illustrated that the age at cracking significantly correlated with the restrained strain and the stress development, which were influenced by the relative humidity of the cementitious composite. The higher relative humidity that was maintained in the WSP specimen at an early age was due to the modified pore solution's viscosity. Both the viscosity and the surface tension of the pore solution were two major factors that affected the stress rate. A higher internal relative humidity and a lower surface tension contributed to a smaller stress rate. Nevertheless, the computed crack strain of the WSP showed no relationship to the cracking tendency.     

碳酸钙晶须对混杂纤维增强高延性水泥基复合材料力学性能的影响

为了探究碳酸钙晶须对钢纤维/PVA混杂纤维增强高延性水泥基复合材料(HyFRHDCC)力学性能的影响,利用2%体积掺量的廉价碳酸钙晶须替代部分纤维,研究了不同纤维掺量HyFRHDCC的压缩性能和拉伸性能,利用扫描电子显微镜观察了HyFRHDCC的微观结构。研究结果表明,引入碳酸钙晶须能够提高HyFRHDCC的初裂拉伸应变和峰前压缩韧性;在1.5%PVA+0.25%钢纤维HyFRHDCC中掺入2%碳酸钙晶须可以改善材料的拉伸性能;当PVA纤维减少至1%时,HyFRHDCC出现了明显的应变软化行为。微观形貌分析发现,碳酸钙晶须能够通过裂纹偏转、晶须拔出以及裂缝桥联等微观机制改善HyFRHDCC的应变硬化行为。     

高Nb-TiAl合金的凝固组织与力学性能研究

研究了Al含量变化对高Nb-TiAl合金的凝固组织与力学性能的影响.结果表明:随着Al含量的增加,TiAl合金晶粒尺寸呈增加趋势;当Al含量为45.7%时,凝固过程中局部区域发生包晶转变,使晶粒尺寸显著增大;室温及700℃高温拉伸强度随着Al含量的增加而呈增加的趋势,但发生包晶转变致使室温及700℃高温拉伸强度下降约200MPa;Al含量对延伸率不敏感,持久性能随Al含量的增加呈增加趋势.为控制铸锭凝固后的组织与力学性能,尽量避开包晶转变区,合金中Al含量应低于45.7%.     

Multiple effects of nano-SiO2 and hybrid fibers on properties of high toughness fiber reinforced cementitious composites with high-volume fly ash

This article explores multiple effects of nano-SiO₂ and hybrid fibers on the flowability, microstructure and flexural properties of high toughness fiber reinforced cementitious composites. Only a little negative influences of nano-SiO₂ and hybrid fibers on the flowability are observed. SEM and MIP analysis reveal that nano-SiO₂ results in much smaller pore size in the composites. However, the porosity increases gradually with nano-SiO₂ addition. Three-point bending test results show that nano-SiO₂ increases the flexural strength of the composites with nearly equivalent deformability, but higher strength of the matrix leads to wider cracks. Due to larger volume fraction and higher modulus, hybrid fibers effectively mitigate this adverse influence on crack width and further enhance the flexural strength. The composites reinforced with 1.4% steel fiber and 2.5% polyvinyl alcohol (PVA) fiber exhibit the best flexural properties in the test. Finally, a simplified model is proposed to illustrate the reinforced mechanism of steel-PVA fibers.     

Effect of plastic coating on the sensory properties of fibreboard-based packaging materials in microwave oven heating

The effects of the type and thickness of plastic coating on the migration of off-odours and off-flavours from fibreboard materials to certain model foodstuffs were studied in microwave oven heating. Correlations between sensory, physical and chemical properties of fibreboard materials were also determined. The plastic coating served as a very good barrier to the transfer of off-flavours into foodstuffs. Polyester coating prevented the migration of off-flavours, whereas polyethylene and polypropylene were effective only in certain cases. With the last two plastics, the thickness of the coating layer also affected the amount of off-flavours migrating. Generally, the sensory properties of the materials did not correlate with either the melting behaviour of the plastic coating or the amount of volatile compounds generated.     

超高韧性水泥基复合材料碳化与渗透性能试验研究

对超高韧性水泥基复合材料(UHTCC) 进行了快速碳化、预裂后的快速碳化、渗透性、快速氯离子渗透试验及自由氯离子含量测定, 研究了不同龄期UHTCC 的抗碳化性能和渗透性能。试验结果表明, 在无裂缝状态下, UHTCC 的抗碳化性能与同强度普通混凝土相当, 但在相同荷载预裂后, UHTCC 裂缝处的碳化深度仅为对比混凝土的30 %～40 %; UHTCC 抗渗性能优于同强度普通混凝土, 且随着龄期增长优势更明显, 56 天龄期的渗透系数约为对比混凝土的35 %; 快速氯离子试验和自由氯离子含量测定得到的氯离子渗透系数均表明, UHTCC 具有明显优于普通混凝土的抵抗氯离子渗透性能。