Mechanical and durability properties of high performance concretes containing supplementary cementitious materials

An experimental investigation was carried out to evaluate the mechanical and durability properties of high performance concretes containing supplementary cementitious materials in both binary and ternary systems. The mechanical properties were assessed from the compressive strength, whilst the durability characteristics were investigated in terms of chloride diffusion, electrical resistivity, air permeability and water absorption. The test variables included the type and the amount of supplementary cementitious materials (silica fume, fly ash and ground granulated blast-furnace slag). Portland cement was replaced with fly ash up to 40%, silica fume up to 15% and GGBS up to a level of 70%.The results confirmed that silica fume performs better than other supplementary cementitious materials for the strength development and bulk resistivity. The ternary mixes containing ground granulated blast-furnace slag/fly ash and silica fume performed the best amongst all the mixes to resist the chloride diffusion. The mix containing fly ash showed favourable permeation results. All the ternary combinations can be considered to have resulted in high performance concretes with excellent durability properties.     

Strength and drying shrinkage properties of self-compacting concretes incorporating multi-system blended mineral admixtures

Drying shrinkage can be a major reason for the deterioration of concrete structures. The contraction of the material is normally hindered by either internal or external restraints so that tensile stresses are induced. These stresses may exceed the tensile strength and cause concrete to crack. The present study investigated compressive strength and particularly drying shrinkage properties of self-compacting concretes containing binary, ternary, and quaternary blends of Portland cement, fly ash (FA), ground granulated blast furnace slag (GGBFS), silica fume (SF), and metakaolin (MK). For this purpose, a total of 65 self-compacting concrete (SCC) mixtures were prepared at two different water to binder ratios. It was observed that drying shrinkage lessened with the use of FA, GGBFS, and MK while incorporation of SF increased the drying shrinkage.     

一种改善新老混凝土修补界面长期性能的方法

修补后新老混凝土能否很好地共同工作 ,主要取决于新老混凝土的界面粘结性能。新老混凝土界面良好的耐久性是保证补强加固后混凝土耐久性的关键。研究了采用不同新混凝土和界面剂修补时界面的 7d、2 8d、12 0d、1a以及 3a龄期的粘结强度。研究结果表明 ,新混凝土采用高掺量粉煤灰混凝土 (4 0 % ) ,虽然界面的短龄期强度较低 ,但随着混凝土修补龄期的增长 ,界面粘结强度显著提高 ,尤其在使用粉煤灰砂浆界面剂时 ,界面的粘结强度增加更明显     

高掺量混合材高强水泥的研究

制备了1种高掺矿渣，粉煤灰，石灰石的高强复合水泥，研究了粉磨方式，石膏品种与掺量，外加剂，矿渣民粉煤灰掺量比对复合水泥性能的影响及相应的混凝土的性能，通过微量热仪，XRD，DTA，SEM分析了复合水泥的水化放热特性及水化产物。     

Properties of self-compacting concretes made with binary,ternary, and quaternary cementitious blends of fly ash,blast furnace slag,and silica fume

Self-compacting concretes (SCCs) have brought a promising insight into the concrete industry to provide environmental impact and cost reduction. However, the use of ternary and especially quaternary cementitious blends of mineral admixtures have not found sufficient applications in the production of SCCs. For this purpose, an experimental study was conducted to investigate properties of SCCs with mineral admixtures. Moreover, durability based multi-objective optimization of the mixtures were performed to achieve an optimal concrete mixture proportioning. A total of 22 concrete mixtures were designed having a constant water/binder ratio of 0.44 and a total binder content of 450 kg/m³. The control mixture included only a Portland cement (PC) as the binder while the remaining mixtures incorporated binary, ternary, and quaternary cementitious blends of PC, fly ash (FA), ground granulated blast furnace slag (S), and silica fume (SF). Fresh properties of the SCCs were tested for slump flow diameter, slump flow time, L-box height ratio, and V-funnel flow time. Furthermore, the hardened properties of the concretes were tested for sorptivity, water permeability, chloride permeability, electrical resistivity, drying shrinkage, compressive strength, and ultrasonic pulse velocity. The results indicated that when the durability properties of the concretes were taken into account, the ternary use of S and SF provided the best performance.     

Influence of pozzolan from various by-product materials on mechanical properties of high-strength concrete

This paper presents experimentally investigated the effects of pozzolan made from various by-product materials on mechanical properties of high-strength concrete. Ground pulverized coal combustion fly ash (FA), ground fluidized bed combustion fly ash (FB), ground rice husk–bark ash (RHBA), and ground palm oil fuel ash (POFA) having median particle sizes less than 11 μm were used to partially replace Portland cement type I to cast high-strength concrete. The results suggest that concretes containing FA, FB, RHBA, and POFA can be used as pozzolanic materials in making high-strength concrete with 28-day compressive strengths higher than 80 MPa. After 7 days of curing, the concretes containing 10–40% FA or FB and 10–30% RHBA or POFA exhibited higher compressive strengths than that of the control concrete (CT). The use of FA, FB, RHBA, and POFA to partially replace Portland cement type I has no significant effect on the splitting tensile strength and modulus of elasticity as compared to control concrete or silica fume concretes. This results suggest that the by-products from industries can be used to substitute Portland cement to produce high-strength concrete without alteration the mechanical properties of concrete.     

掺超细粉煤灰活性粉末混凝土的研究

采用525普能硅酸盐水泥、硅灰、超细粉煤灰、高效减水剂和标准砂等原材料及湿热养护工艺,可配制出抗压强度达200MPa的活性粉末混凝土,在掺入一定量的钢纤维后,活性粉末混凝土的抗压强度近250MPa,抗折强度达45MPa,对超细粉煤灰掺量、水胶比、砂胶比和钢纤维掺量等因素于掺超细粉煤灰活性粉末混凝土抗折、抗压强度的影响进行了详细的讨论。     

Sulfate resistance of the cement materials based on the modified silica fume

The object of the study was the influence of chemically modified silica fume (MSF) on the sulfate resistance of cement-based materials. MSF is a liquid product prepared from a suspension of silica fume and a water solution of a reactant under the defined composition of suspension, defined ambient temperature and time of procedure. MSF is added into mortar or concrete mixtures instead of water in the quantities needed for the desired consistency. The results obtained at the application of MSF shows a significant increase of sulfate resistance of materials based on Portland cement slag blends and slag binder. This positive effect represents a further beneficial potential of MSF that has already been shown as an effective hardening accelerator together with its ability to increase the acidic resistance of materials based on Portland cement slag blends and slag binder.     

Effect of electric arc furnace dust on the properties of OPC and blended cement concretes

This paper presents results of a study conducted to evaluate the mechanical properties and durability characteristics of ordinary Portland cement (OPC) and blended cement (silica fume and fly ash) concrete specimens prepared with electric arc furnace dust (EAFD). Concrete specimens were prepared with and without EAFD. In the silica fume cement concrete, silica fume constituted 8% of the total cementitious material while fly ash cement concrete contained 30% fly ash. EAFD was added as 2% replacement of cement in the OPC concrete and 2% replacement of the total cementitious content in the blended cement concretes. Mechanical properties, such as compressive strength, drying shrinkage, initial and final setting time, and slump retention were determined. The durability characteristics were evaluated by measuring water absorption, chloride permeability, and reinforcement corrosion. The initial and final setting time and slump retention increased due to the incorporation of EAFD in both OPC and blended cement concretes. The drying shrinkage of EAFD cement concrete specimens was more than that of concrete specimens without EAFD. The incorporation of EAFD was beneficial to OPC concrete in terms of strength gain while such a gain was not noted in the blended cement concretes. However, the strength differential between the blended cement concretes with EAFD and the corresponding concretes without EAFD was not that significant. The water absorption and chloride permeability, however, decreased due to the incorporation of EAFD in both the OPC and blended cement concretes. The corrosion resistance of OPC and blended cement concrete specimens increased due to the addition of EAFD.     

Characteristics of lightweight concrete containing mineral admixtures

This research investigates the properties of fresh and hardened concretes containing locally available natural lightweight aggregates, and mineral admixtures. Test results indicated that replacing cement in the structural lightweight concrete developed, with 5–15% silica fume on weight basis, caused up to 57% and 14% increase in compressive strength and modulus of elasticity, respectively, compared to mixes without silica fume. But, adding up to 10% fly ash, as partial cement replacement by weight, to the same mixes, caused about 18% decrease in compressive strength, with no change in modulus of elasticity, compared to mixes without fly ash. Adding 10% or more of silica fume, and 5% or more fly ash to lightweight concrete mixes perform better, in terms of strength and stiffness, compared to individual mixes prepared using same contents of either silica fume or fly ash.     

Sulfate resistance of blended cements containing fly ash and rice husk ash

In this paper, the sulfate resistance of mortars made from ordinary Portland cement containing available pozzolans viz., fly ash and ground rice husk ash (RHA) was studied. Class F lignite fly ash and RHA were used at replacement dosages of 20 and 40% by weight of cement. Expansion of mortar prisms immersed in 5% sodium sulfate solution and the change in the pH values of the solution were monitored. The incorporation of fly ash and RHA reduced the expansion of the mortar bars and the pH values of the solutions. RHA was found to be more effective than fly ash. Examination of the fractured surface of mortar prisms, after a period of immersion, by scanning electron microscopy confirmed that sulfate attack of blended cement mortars was restricted owing to the reductions in calcium hydroxide and C/S ratio of the C–S–H gel in the blended cement mortar. In comparison to Portland cement mortar, less calcium sulfate and much less ettringite formations were found in the mortars made from blended cement containing RHA. The amounts of calcium sulfate and ettringite found in the blended cement mortar containing fly ash were also small but were slightly more than those of RHA mortar. Up to 40% of Portland cement could be replaced with these pozzolans in making blended cement with good sulfate resistance.     

Experimental investigation on mechanical properties of binary and ternary blended pervious concrete

The purpose of the investigation was to study the effect of binary and ternary blends of cement on the mechanical properties of pervious concrete (PC) specimen through destructive (DT) and non-destructive testing (NDT). Various combinations of fly ash (FA), limestone powder (LP), metakaolin (MK), and silica fume (SF) as mineral admixtures have been investigated to partially replace the cement up to 30% by weight in PC. Standard cube specimens of size 150 mm × 150 mm × 150 mm of binary and ternary blends of mineral admixture of pervious concrete were prepared to conduct standard compressive strength test and split tensile test at 7 and 28 days of curing. The ultrasonic pulse velocity (UPV) test and Rebound Hammer test were used as a non-destructive testing tool to substantiate the robustness of PC and to determine the approximate mechanical properties where other destructive testing tools are not feasible in case of in-place pervious pavements. Overall the pervious concrete made with LP based ternary blends (PLM and PLS) were found to perform better than FA based ternary blends (PFM and PFS) and control mix (PC) in destructive and non-destructive testing.     

Influence of dry and wet curing conditions on compressive strength of silica fume concrete

This paper reports a part of an ongoing laboratory investigation in which the compressive strength of silica fume concrete is studied under dry and wet curing conditions. In the study, a total of 48 concretes, including control Portland cement concrete and silica fume concrete, were produced with four different water–cement ratios (0.3, 0.4, 0.5, 0.6), three different cement dosages (350, 400, 450 kg/m³) and three partial silica fume replacement ratios (10%, 15%, 20%). A hyperplastisizer was used in concrete at various quantities to provide and keep a constant workability. Three cubic samples produced from fresh concrete were demoulded after a day; then, they were cured at 20±2 °C with 65% relative humidity (RH), and three other cubic samples were cured at 20±2 °C with 100% RH until the samples were used for compressive strength measurement at 28 days. The comparison was made on the basis of compressive strength between silica fume concrete and control Portland cement concrete. Silica fume concretes were also compared among themselves. The comparisons showed that compressive strength of silica fume concrete cured at 65% RH was influenced more than that of Portland cement concrete. It was found that the compressive strength of silica fume concrete cured at 65% RH was, at average, 13% lower than that of silica fume concrete cured at 100% RH. The increase in the water–cementitious material ratios makes the concrete more sensitive to dry curing conditions. The influence of dry curing conditions on silica fume concrete was marked as the replacement ratio of silica fume increased.     

Possibilities of a novel use of silica fume in mineral binding systems

The aim of the study was to estimate the conditions of the effectiveness of a novel use of silica fume in concrete. This represents chemically modified silica fume (MSF). The activity of MSF evidently is predominantly based on the production of calcium silicate hydrates in the binding systems resulting in the advantageous densifying of the formatted pore structure and in the increase in strength of the material. The results obtained have shown that MSF is a very effective admixture for the acceleration of hardening of mineral binder based materials. A very important fact is its high activity in the binding systems based on Portland cement slag blends with very low Portland cement content and on basic blast furnace slag alone. Therefore, MSF seems to be a prospective component for development for blend binders with very low content in Portland cement and untraditional binders based only on solid waste materials, predominantly containing calcium silicate and alumino silicate constitutions. MSF seems to be worthy of more detailed study on the effective utilisation of its positive effects.     

NaCl除冰盐作用下混凝土的抗冻能力分析

通过存质量浓度为3.5%的NaCl溶液中的冻融循环试验,测试了普通混凝土、引气混凝土、粉煤灰混凝土和硅灰混凝土的相对动弹性模量和质量损失率,分析了不同混凝土的抗盐冻的能力.结果表明:适当的引气能够明显改善混凝土的抗盐冻性能,掺加20%粉煤灰时,混凝土仍具有较高的抗盐冻能力,掺量达到40%时混凝土的抗盐冻性能明显下降,掺加10%硅灰明显提高混凝土的抗盐冻能力.     

Genetic algorithm for cost optimization of modified multi-component binders

This paper describes the application of a genetic algorithm for the cost optimization of a modified multi-component binder (MMCB). An MMCB comprised of Portland cement (NPC), finely ground mineral additives (fly ash, ponded ash or granulated blast furnace slag), and a highly reactive powder component (usually silica fume, SF) was modified by a superplasticizer (SP). Strength models based on the experimental results were developed. The present work is oriented to the minimization of the MMCB cost for specific strength levels with the help of a changing range genetic algorithm (CRGA) to handle the nonlinear constraints imposed by the MMCB models. The developed CRGA is based on an approach that adaptively shifts and shrinks the size of the search space to the feasible region. The application of CRGA helps to minimize the cost of MMCB with a low resolution of the binary representation scheme and without additional computational efforts.     

粉煤灰、矿渣及硅灰对水泥胶砂流动性及早期强度的影响

本文在试验的基础上研究了矿物掺合料单掺和复掺时对水泥胶砂流动性及1d早期强度的影响。试验结果表明,与不掺掺合料的基准胶砂相比,矿物掺合料的使用可以提高胶砂的流动度,但同时极大地降低了胶砂的早期强度。与单掺粉燥灰的胶砂相比,多种矿物掺合料复掺可以提高胶砂的1d强度,但会降低胶砂的流动性。     

Coarse blast furnace slag as a cementitious material,comparative study as a partial replacement of Portland cement and as an alkali activated cement

The cementitious performance of a coarse granulated blast furnace slag, 2900 cm²/g, was investigated in concretes of 230, 280 and 330 kg binder/m³. First, the slag partially replaced 30%, 50% and 70% of Portland cement, the strength reduced as the amount of slag increased; however, for high binder contents, similar strengths were attained for lower Portland cement contents. Second, the slag was alkali activated with sodium silicate (moduli 1.7 and 2) at 4%, 6% and 8% %Na₂O, the strength increased with the amount of slag in the concrete and developed faster as %Na₂O increased. The microstructures of both type of concretes were dense; however, the strengths of activated slag were superior at similar binder loads, indicating that the hydration products of activated slag are of higher intrinsic strength.     

Compressive strength and stability of sustainable self-consolidating concrete containing fly ash,silica fume,and GGBS

This paper presents the findings of an experimental program seeking to understand the effect of mineral admixtures on fresh and hardened properties of sustainable self-consolidating concrete (SCC) mixes where up to 80% of Portland cement was replaced with fly ash, silica fume, or ground granulated blast furnace slag. Compressive strength of SCC mixes was measured after 3, 7, and 28 days of moist curing. It was concluded in this study that increasing the dosage of fly ash increases concrete flow but also decreases segregation resistance. In addition, for the water-to-cement ratio of 0.36 used in this study, it was observed that the compressive strength decreases compared to control mix after 28 days of curing when cement was partially replaced by 10%, 30%, and 40%of fly ash. However, a fly ash replacement ratio of 20% increased the compressive strength by a small margin compared to the control mix. Replacing cement with silica fume at 5%, 10%, 15%, and 20% was found to increase compressive strength of SCC mixes compared to the control mix. However, the highest 28 day compressive strength of 95.3 MPa occurred with SCC mixes in which 15% of the cement was replaced with silica fume.     

试验方法对混凝土抗氯离子渗透扩散性的影响

采用快速氯离子渗透试验方法,稳态电迁移方法和电导方法,对普通水泥混凝土、轻骨料混凝土及掺粉煤灰、矿渣,硅粉,偏高岭土和稻壳灰的混凝土进行了抗氯离子渗透扩散性试验研究。结果表明,三种方法得到的混凝土抗氯离子渗透扩散性的结论相类似,但在混凝土的氯离子渗透扩散性较低时,相互之间的规律性不大明显。ASTMC1202在许多情况下仍然可以采用,特别适用于不掺混凝合的混凝土。