Coupled effect of time and temperature on variations of plastic viscosity of highly flowable mortar

Self-consolidating concrete (SCC) is being increasingly used as construction material for its workability. However, the rheological properties of such concrete, which is made with significant concentration of high-range water-reducing admixture (HRWRA), depend in most cases on the casting temperature of the material. The study presented herein aimed at evaluating the coupled influence of time and temperature on the variations of plastic viscosity (µ) of micro mortar made with polymelamine (PMS), polynaphtalene (PNS) and polycarboxylate (PCP) polymer. In total, seven micro mortar mixtures proportioned with various binder compositions and water-to-binder ratios of 0.42 and 0.53 were prepared at 10 to 33 °C. Test results show that the plastic viscosity varies linearly with the coupled effect of time and temperature for mixtures made with PNS or PMS HRWRA. However, for mixtures made with PCP-HRWRA, both temperature and mixture proportioning have influence on the variation of viscosity with time.     

偏高岭土对高流动性钢纤维混凝土早期力学性能和细观结构的影响

为了提高泵送混凝土流动性及早期力学性能,降低水泥用量,本文研究了高流动性偏高岭土和钢纤维复合混凝土的流动性、抗压和抗拉强度、弹性模量、破坏形态和微观结构,并在此基础上评价了偏高岭土和钢纤维对混凝土性能的影响。结果表明,随着钢纤维和偏高岭土含量的增加,浆体的流动性降低,偏高岭土影响更加显著。偏高岭土提高了钢纤维混凝土养护7 d后的抗压强度、抗拉强度和弹性模量,钢纤维对残余拉伸强度和裂纹扩展有明显的影响。通过扫描电镜(SEM)观察与X射线衍射(XRD)分析,偏高岭土的添加使试样内部产生了更稳定的水化硅酸钙(CSH)凝胶、单硫型水化硫铝酸钙(AFm)和高硫型水化硫铝酸钙(AFt)等物质。这些产物减少了孔隙和缺陷的产生,增强了界面过渡区的粘结力。由于偏高岭土和钢纤维对和易性的影响机制分别为增加黏度和提升浆体的抗剪切能力,本质上都为阻碍各组分的相对运动,所以二者在降低混凝土流动性方面具有耦合作用。偏高岭土与钢纤维影响混凝土力学性能的阶段不同,前者在未开裂阶段,后者在开裂阶段。     

含浆量对再生混凝土性能及强度的影响

再生集料表面包裹着一层硬化水泥砂浆、导致再生混凝土的强度变化较复杂。利用集料的吸水率指标来探讨如何利用吸水率、取代率来推算含浆量以及不同含浆量的再生集料对混凝土7d、28d强度;再生混凝土的强度与灰水比的线性关系和工作性能的影响。     

State of the art for fly ash uses in concrete

An overview of accomplishments in recent research and of attractive further work for improvements of the uses of fly ash in concrete is presented.Improved workability of fresh concrete, reduction of peak curing temperatures and increase of the denseness of hardened concrete are being recognized as attainable advantages in practice. Also pozzolanic reactivity as protection against reactions with alkali-susceptible aggregates is of increasing interest.There is in research a trend towards more work about the characterisation of fly ashes in relation to chemical composition and mineralogy structure. Also their impact on the rheology of fresh cement paste, on the energetics of the hydrating system and on the microstructure of hardened cement paste is increasingly being studied. More interaction with other branches of materials science is still desirable.The practice-research relations are demonstrated by experience with use of fly ash in the concrete of a major bridge construction in Denmark. Coherent research and development efforts are found commendable.     

UHPC浆体的工作性和流变性与颗粒膜层厚度的关系

建立超高性能混凝土(UHPC)浆体的工作性和流变性之间的关系可从理论上研究其工作性变化规律。本文以颗粒膜层厚度为UHPC浆体的工作性的综合衡量指标,设计了正交试验,研究水胶比、超细粉煤灰替代率和硅灰掺量对UHPC浆体的工作性与流变性的影响。根据流动度和流变性测试结果,分析了水胶比和超细粉煤灰替代率的共同作用对UHPC浆体的工作性与流变性的影响,探究了UHPC的净浆与砂浆的工作性关系,基于浆膜层厚度给出了UHPC砂浆的工作性与流变性的关系式。研究结果表明:水胶比是UHPC浆体的工作性与流变性的最主要影响因素,水胶比、超细粉煤灰替代率和硅灰掺量提高均造成UHPC浆体的颗粒表面膜层厚度增大;水胶比和超细粉煤灰替代率的共同作用下,UHPC浆体的流动度和黏度系数具有相关性。     

锂渣掺量对水泥-减水剂浆体流变特性和混凝土性能的影响

本文研究了锂渣掺量对水泥-减水剂浆体流变特性、新拌混凝土工作性及硬化混凝土强度的影响。从紧密堆积理论和固体颗粒体积分数角度解释了锂渣掺量对水泥-减水剂浆体流变性能的影响。结果表明：锂渣水化初始的屈服应力和塑性黏度均随锂渣掺量的增加而增大，流变性能劣化。新拌混凝土的工作性与锂渣掺量呈负相关；随锂渣掺量的增加，7 d抗压强度不断降低，28 d抗压强度呈现出先增后降的趋势。     

Effects of metallic monomer powders on the mechanical properties of hardened polyester and acrylic polymer concrete

To investigate the effects of three metallic monomer powders on polyester‐ and acrylic‐hardened polymer concretes, polymer concretes incorporating different levels of these materials were investigated for the properties of hardened polymer concrete. The mix design was made and optimized for workability and strength, depending on the resin viscosity, the intended use, and the additional quantities of these polymeric materials. The investigated properties included the compressive strength, flexural strength, and bond strength of hardened polymer concrete. It was concluded that these polymeric materials offer the possibility of improving the properties of polyester‐ and acrylic‐hardened polymer concretes. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3106–3113, 2006     

Effect of limestone filler BET(H2O)-area on the fresh and hardened properties of self-compacting concrete

This paper presents a study on the use of limestone fillers with different specific surface area and their effect on the fresh and hardened properties of self-compacting concrete (SCC). The surface area was determined by a simplified BET method using water vapour as adsorbate. A rheometer and a slump flow test were used to measure the flowability of fresh concrete. A concrete dilatometer was used to measure the autogenous shrinkage, and a ring-test for the plastic cracking tendency. The compressive strength was determined at 28 days. It was found that the measure of BET(H₂O)-area can be used to evaluate the water requirement for constant workability of the SCC, where a change in BET(H₂O)-area of 1000 m²/kg corresponds to approximately 0.8% in moisture content. The results showed that filler with a large area will result in an increased autogenous shrinkage, decreased evaporation, lower plastic cracking tendency, and a higher compressive strength. With additional water the results was the opposite.     

Moisture sensitivity of polyester and acrylic polymer concretes with metallic monomer powders

To evaluate the moisture sensitivity of polyester and acrylic polymer concretes with commercial metallic monomer powders, polymer concretes containing different levels of these powders were investigated with respect to the properties of hardened polymer concrete. The mix design was made and optimized for workability, strength, and economy, which depended on the resin viscosity, the intended use, and the additional quantities of the polymeric materials. The investigated properties included the compressive and flexural strengths of hardened polymer concrete. These polymeric materials offer the possibility of using wet aggregates in polyester and acrylic polymer concrete construction. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Properties of concrete containing waste glass

In our study, in which waste glass (WG) is considered as coarse aggregates in the concrete, WG was used reduced to 4-16 mm in proportions of 0-60% in the production of PKÇ/B 32.5/R type cement. The effects of WG on workability and strength of the concrete with fresh and hardened concrete tests were analyzed. As a result of the study conducted, WG was determined not to have a significant effect upon the workability of the concrete and only slightly in the reduction of its strength. Waste glass cannot be used as aggregate without taking into account its ASR properties. As for cost analysis, it was determined to lower the cost of concrete productions. Our study was an environmental one in consideration to the fact that WG could be used in the concrete as coarse aggregates without the need for a high cost or rigorous energy.     

Exploitation of poor Greek kaolins: strength development of metakaolin concrete and evaluation by means of k-value

In this paper, the effect of metakaolin on concrete properties is investigated. A poor Greek kaolin was thermally treated at defined conditions, and the produced metakaolin was superfine ground. In addition, a commercial metakaolin of high purity was used. Eight mixture proportions were used to produce high-performance concrete, where metakaolin replaced either cement or sand in percentages of 10% or 20% by weight of the control cement content. The strength development of metakaolin concrete was evaluated using the efficiency factor (k-value). The produced metakaolin as well as the commercial one imparts a similar behavior with respect to the concrete strength. Both metakaolins exhibit very high k-values (close to 3.0 at 28 days) and are characterised as highly reactive pozzolanic materials that can lead to concrete production with an excellent performance.     

Effect of wash water and underground water on properties of concrete

This study deals with the effect of different types of mixing water on properties of mortar and concrete such as compressive strength, setting times and workability. Water used for mortar and concrete include tap water, underground water and wash water from mixer washout operations in a ready-mixed concrete plant. This study analyzes the quality of these types of water. Then, tests were conducted on mortar and concrete. All the underground water and wash water tested meet the ASTM C94 requirements on mixing water for ready-mixed concrete. Concrete mixed with bottom wash water gave a shorter setting time and a lower flowability since bottom wash water contains some residual cement. Neither top and middle wash waters nor underground water significantly affected slump of fresh mortar. The compressive strength of concrete mixed with wash water or underground water is as good as that with tap water. Therefore, it is suggested that underground water should be considered as mixing water for concrete and wash water be recycled where tap water resources are scarce. However, it is advised that other properties such as durability or shrinkage be studied before use.     

Effects of local metakaolin addition on rheological and mechanical performance of self-compacting limestone cement concrete

Various mineral additions are used in the manufacture of self-compacting concrete (SCC) to reduce the cement content and hence the CO₂ emissions and also to enhance the performance of concrete. In this paper, the results of fresh and hardened properties of self-compacting limestone cement mortar (SCLCM) and concrete (SCLCC) with metakaolin (MK) as cement replacement are reported. SCLCM properties investigated include spread flow, V-funnel flow time, yield stress, plastic viscosity and heat evolution. SCLCC fresh properties include slump flow, V-funnel flow time, J-Ring, L-Box and sieve segregation. Compressive strength of the hardened SCLCC was measured at the ages of 1, 3, 7, 28, 90, and 180?days. Moreover, water porosity, water absorption by capillarity and dynamic modulus of elasticity (E_d) tests were conducted. Test results indicated that the produced MK is of sufficient pozzolanic activity and contributes to improve the performances of concrete in particular at later stages. The addition of MK to SCLCM mixes exhibits lower heat evolution, lower yield stress, higher plastic viscosity and higher V-funnel flow time. The addition of MK to SCLCC mixes improves the rheological properties (flowability, passing ability and segregation resistance) as well as the mechanical and durability performance.     

引气剂对混凝土性能的影响研究

研究了引气剂对混凝土工作性、力学性能以及抗冻融性能的影响。结果表明：通过掺加引气剂增加新拌混凝土含气量,可以改善混凝土的工作性。同时混凝土的冻融耐久性得以改善,气孔间距系数越小,混凝土的冻融耐久性指数就越大。但是,引气剂的掺入降低了混凝土的强度,硬化混凝土平均孔径越小,越有利于减小因引气而造成的抗压强度损失。     

Effects of retempering on consistency and compressive strength of concrete subjected to prolonged mixing

In this study, effects of prolonged mixing and four different retempering processes on some properties of fresh and hardened concrete, such as temperature, slump loss, and strength, were investigated. Two types of concrete mixtures with different compression strength having 15 cm initial slump were produced in a laboratory mixer. After mixing for 5 min at 20 rpm speed to ensure homogeneity, the mixing was continued at 4 rpm for a period of up to 4 h to simulate the prolonged agitation of ready-mixed concrete in truck mixers. Concrete samples were taken out of the mixer at the end of first, second, third, and fourth hour for estimating the effects of prolonged mixing on properties of fresh concrete. For restoring the initial workability, four different retempering methods were used and their effects on properties of concrete were investigated. Results show that compared to the untempered concrete mixtures, those tempered with solutions prepared by 3% or 4.5% solid superplasticizer by mass of retempering water had significantly less loss of 28-day compressive strength.     

Effect of partial replacement of geopolymer binder materials on the fresh and mechanical properties: A review

The growth of demand for concrete raises concerns about the consumption of natural resources and ordinary Portland cement. Geopolymer composites show promise as a sustainable alternative for conventional cement concrete. Considering the wide range of potential geopolymer composites applications (including suitability for transportation infrastructure, underwater applications, repair and rehabilitation of structures as well as recent developments in 3D printing), the desired fresh and mechanical properties of the geopolymer composite may vary between applications: for example, rapid setting can be a merit for certain applications and a demerit for others. Therefore, the desired fresh and mechanical properties (e.g., workability, setting time, compressive strength, etc.) can be controlled for a given geopolymer source material through its partial substitution by natural or by-product materials. Recognizing the critical role of various replacement materials in enhancing the potential applications of geopolymer composites, the present review was undertaken to quantify and understand the effect of partial replacement by fly ash, metakaolin, kaolin, red mud, slag, ordinary Portland cement, and silica fume on the setting time, workability, compressive strength and flexural strength of various source materials addressed in the literature. The review also provides insights into research gaps in the field to promote future research.     

Yield stress and viscosity equations for mortars and self-consolidating concrete

The rheological behavior of flowable concrete, such as self consolidating concrete is closely influenced by concreting temperature and the elapsed time. The variation of the plastic viscosity and the yield stress with the elapsed time and temperature must be accurately quantified in order to forecast the variation of workability of cement-based materials. A convenient method to study the variation of these rheological parameters is proposed, using the mortar of the concrete. This latter is designed from the concrete mixture, taking in account the liquid and solid phases with a maximum granulometry of 315 μm. Different SCC and mortars proportioned with two types of high range water reducing admixtures (HRWRA) were prepared at temperatures ranging from 10 to 33 °C. Test results indicates that the yield stress and the plastic viscosity of the mortar mixtures vary in a linear way with the elapsed time while an exponential variation of these rheological parameter is seen on SCC. In order to enhance robotization of concrete, general equations to predict the variations of the yield stress and plastic viscosity with time are proposed, using the corresponding mortar initial yield stress and plastic viscosity. Such equations, derived from existing models, can easily be employed to develop concrete design software. Experimental constants which are related to the paste fluidity or the aggregates proportioning can be extracted from a database created with either mortar or aggregates test results.     

Eco-friendly concretes with reduced water and cement contents — Mix design principles and laboratory tests

The major environmental impact of concrete is caused by CO₂-emissions during cement production. Great potential for reducing the impact is seen especially for concretes with normal strength. The use of superplasticizers and highly reactive cements as well as optimization of particle-size distribution and reduction in water content allows a significant reduction in Portland cement clinker in the concrete. Essential is the addition of mineral fillers (e.g. limestone powder) to provide an optimal paste volume. In addition, the already practicable substitution of secondary raw materials like fly-ash or furnace-slag for cement clinker is an appropriate option which is however limited by the availability of these resources.In several test series the fresh and hardened concrete properties of concretes with reduced water and cement contents were investigated, especially their workability, strength development, design-relevant mechanical properties as well as durability aspects such as carbonation. It was shown that concretes with cement clinker and slag contents as low as 150 kg/m³ were able to meet the usual requirements of workability, compressive strength (approx. 40 N/mm²) and mechanical properties. The carbonation depth of concretes with 150-175 kg/m³ clinker and slag was equal or lower than the depth of conventional reference concretes for exterior structures. The ecological advantages were identified, using environmental performance evaluation. A reduction of up to 35% in environmental impact was calculated compared with conventional concrete and of more than 60% with granulated blast-furnace slag. Practical application was verified by means of full-scale tests in a precast and ready-mix concrete plant.     

Effects of emulsifiers on properties of poly(styrene-butyl acrylate) latex-modified mortars

Two styrene-butyl acrylate copolymer latices having the same chemical components but different emulsifiers were synthesized under the same reaction conditions, and their effects on such properties as workability, air content, compressive strength, flexural strength and water absorption of fresh and hardened polymer-modified mortars were assessed and discussed. From the tested properties of the polymer-modified mortars, it is concluded that a polymeric emulsifier provides a much more positive effect on the properties of the polymer-modified mortars than a low-molecular emulsifier.     

混凝土中粉煤灰工程效应的估算和分析

粉煤灰对混凝土工作性、强度发展和耐久性的影响,即取决于粉煤灰的材料品质,又取决于混凝土的组成结构。等工作性下,粉煤灰混凝土与基准混凝土的需水量比、28d强度比以及某项耐久性指标比值可以表征或定义混凝土中粉煤灰的一系列工程效应,即塑化效应、固化效应和免疫效应。本文就混凝土系统,提出了估算粉煤灰塑化效应和固化效应的方法,并运用粉煤灰工程效应的观点,初步探讨了双掺法中粉煤灰工程效应之间的相互关系。