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.     

Properties of steel fiber reinforced fly ash concrete

This paper reports on a comprehensive study on the properties of concrete containing fly ash and steel fibers. Properties studied include unit weight and workability of fresh concrete, and compressive strength, flexural tensile strength, splitting tensile strength, elasticity modulus, sorptivity coefficient, drying shrinkage and freeze–thaw resistance of hardened concrete. Fly ash content used was 0%, 15% and 30% in mass basis, and fiber volume fraction was 0%, 0.25%, 0.5%, 1.0% and 1.5% in volume basis. The laboratory results showed that steel fiber addition, either into Portland cement concrete or fly ash concrete, improve the tensile strength properties, drying shrinkage and freeze–thaw resistance. However, it reduced workability and increase sorptivity coefficient. Although fly ash replacement reduce strength properties, it improves workability, reduces drying shrinkage and increases freeze–thaw resistance of steel fiber reinforced concrete. The performed experiments show that the behaviour of fly ash concrete is similar to that of Portland cement concrete when fly ash is added.     

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.     

Incorporating ground glass in self-compacting concrete

This research investigated the feasibility of using ground glass in self-compacting concrete (SCC). The ground glass was used as a partial replacement for both the cement and fine aggregate.The results show that to keep the filling ability constant, the inclusion of ground glass would require an increase in water/powder ratio and a reduction in superplasticizer dosage. These did not change the passing ability, but degraded the consistence retention and hardened properties such as strength but not to a prohibitive extent. This research concludes that SCC with satisfactory fresh properties can be produced by incorporating up to 104 kg/m³ ground glass, replacing about 10% cement and 10% sand, without the need for viscosity modifying agent (VMA).The successful completion of this study can lead to the application of ground glass in SCC, thus widening the types of additions available for SCC, saving landfill and reducing CO₂ emissions by the use of less cement and sand.     

大掺量矿物掺合料自密实混凝土抗碳化性能研究

设计了单掺粉煤灰和复掺粉煤灰与矿渣微粉的3个系列自密实混凝土试件.通过快速碳化试验、吸水试验,研究单掺粉煤灰和复掺粉煤灰与矿渣微粉对自密实混凝土抗碳化性能的影响.结果表明:当粉煤灰单掺掺量大于40%(质量分数)后,随着粉煤灰掺量的增大,自密实混凝土抗碳化能力迅速下降;粉煤灰与矿渣微粉复掺可显著缓和大掺量粉煤灰自密实混凝土抗碳化性能的下降.矿物掺合料对自密实混凝土抗碳化性能的影响存在正负效应.     

组成及龄期对复合粉煤灰/水泥浆Cl~-结合性能的影响

研究了组成和龄期对粉煤灰/水泥浆体系硬化水泥浆Cl~-结合能力的影响。首先研究了组成和龄期对粉煤灰和水泥二组分体系硬化水泥浆Cl~-结合性能的影响,并且确定了Cl~-结合量最大的组成比。在该硬化水泥浆Cl~-结合量的组成比例下继续以钠钙硅玻璃粉和Ca(OH)_2混合组成取代水泥,并采用正交试验设计,探讨了玻璃粉掺量、细度和Ca(OH)_2掺量对Cl~-结合性能的影响。结果表明,14d和28d龄期时,粉煤灰对水泥取代量为50wt%的硬化水泥浆Cl~-结合能力达到极大值。正交试验结果表明,在10wt%、20wt%、30wt%的三个水平中,玻璃粉的掺量对硬化水泥浆的Cl~-结合量的影响最大,有使硬化水泥浆Cl~-结合能力降低的作用,而Ca(OH)_2具有使Cl~-结合能力增大的作用。但掺加了玻璃粉和Ca(OH)_2的粉煤灰-水泥浆体系硬化水泥浆Cl~-结合量随龄期的延长而下降。从正交试验的结果来看,少量玻璃粉的掺入并配合使用Ca(OH)_2,有望对掺粉煤灰硬化水泥浆的氯离子结合起到促进作用。     

Influence of class F fly ash on the abrasion–erosion resistance of high-strength concrete

This study investigates the abrasion–erosion resistance of high-strength concrete (HSC) mixtures in which cement was partially replaced by four kinds of replacements (15%, 20%, 25% and 30%) of class F fly ash. The mixtures containing ordinary Portland cement were designed to have 28 days compressive strength of approximately 40–80 MPa. Specimens were subjected to abrasion–erosion testing in accordance with ASTM C1138. Experimental results show that the abrasion–erosion resistances of fly ash concrete mixtures were improved by increasing compressive strength and decreasing the ratio of water-to-cementitious materials. The abrasion–erosion resistance of concrete with cement replacement up to 15% was comparable to that of control concrete without fly ash. Beyond 15% cement replacement, fly ash concrete showed lower resistance to abrasion–erosion compared to non-fly ash concrete. Equations were established based on effective compressive strengths and effective water-to-cementitious materials ratios, which were modified by cement replacement and developed to predict the 28- and 91-day abrasion–erosion resistance of concretes with compressive strengths ranging from approximately 30–100 MPa. The calculation results are compared favorably with the experimental results.     

The effect of silica fume and high-volume Class C fly ash on mechanical properties,chloride penetration and freeze–thaw resistance of self-compacting concrete

In this study, cement has been replaced with a Class C fly ash (FA) in various proportions from 30% to 60%. Durability properties of various self-compacting concrete (SCC) mixtures such as, freezing and thawing, and chloride penetration resistance have been investigated besides mechanical properties within the scope of this study. Similar tests were carried out with the incorporation of 10% silica fume (SF) to the same mixtures. Test results indicate that SCC could be obtained with a high-volume FA. Ten percent SF additions to the system positively affected both the fresh and hardened properties of high-performance high-volume FA SCC. Although there is a little cement content, these mixtures have good mechanical properties, freeze–thaw and chloride penetration resistance.     

Effect of fly ash fineness on microstructure of blended cement paste

This research demonstrates the effect of fly ash fineness on pore size and microstructure of hardened blended cement pastes. Two sizes of fly ash, original fly ash and classified fly ash were used to replace Portland cement type I paste. Test results indicated that the pore sizes of hardened blended cement paste were significantly affected by the rate of replacement and the fineness of fly ash. The replacement of cement by original fly ash decreased the pore sizes of blended cement paste and the incorporation of classified fly ash resulted in a further decrease in the pore sizes of blended cement paste. The X-ray diffraction (XRD) results showed that the blended cement paste with classified fly ash was more effective at reducing the intensity of Ca(OH)₂ than that with the original fly ash. The scanning electron microscope (SEM) results revealed that the hardened blended cement paste containing finer fly ash produced a denser structure than the one containing coarser fly ash.     

Hybrid fiber reinforced self-compacting concrete with a high-volume coarse fly ash

This paper presents a study on the fresh and mechanical properties of a fiber reinforced self-compacting concrete incorporating high-volume fly ash that does not meet the fineness requirements of ASTM C 618. A polycarboxylic-based superplasticizer was used in combination with a viscosity modifying admixture. In mixtures containing fly ash, 50% of cement by weight was replaced with fly ash. Two different types of steel fibers were used in combination, keeping the total fiber content constant at 60 kg/m³. Slump flow time and diameter, V-funnel, and air content were performed to assess the fresh properties of the concrete. Compressive strength, splitting tensile strength, and ultrasonic pulse velocity of the concrete were determined for the hardened properties. The results indicated that high-volume coarse fly ash can be used to produce fiber reinforced self-compacting concrete, even though there is some reduction in the concrete strength because of the use of high-volume coarse fly ash.     

Comparison on efficiency factors of F and C types of fly ashes

Fly ashes are obtained from thermal power plants and they are pozzolanic materials, which can act as partial replacement material for both portland cement and fine aggregate. With their economical advantages and potential for improving fresh and hardened concrete performance, they have some benefits for using in concrete industry. In this study, the objective was to find the efficiency factors of Turkish C and F-type fly ashes and to compare their properties. Three different cement dosages were used (260, 320, 400 kg/m³), two different ratios (10% and 17%) of cement reduced from the control concretes and three different ratios (depending on cement reduction ratio) of fly ash were added into the mixtures. At the ages of 28 and 90 days, compressive strength, modulus of elasticity and ultrasound velocity tests were carried out. From the compressive strength results, the k efficiency factors of C and F-type fly ashes were obtained. As a result, it is seen that efficiency factors of the concrete produced by the replacement of F and C type fly ashes with cement increase with the increase in cement dosage and concrete age.     

Effect of W/C ratio on covering depth of fly ash concrete in marine environment

This investigation studied the effect of W/C ratio on covering depth required against the corrosion of embedded steel of fly ash concrete in marine environment up to 4-year exposure. Fly ash was used to partially replace Portland cement type I at 0%, 15%, 25%, 35%, and 50% by weight of cementitious material. Water to cementitious material ratios (W/C) of fly ash concretes were varied at 0.45, 0.55, and 0.65. The 200-mm concrete cube specimens were cast and steel bars with 12-mm diameter and 50 mm in length were inserted in the concrete with the covering depth of 10, 20, 50, and 75 mm. The specimens were cured in water for 28 days, and then placed to the tidal zone of marine environment in the Gulf of Thailand. Subsequently, the concrete specimens were tested for the compressive strength, chloride penetration profile and corrosion of embedded steel bar after being exposed to tidal zone for 2, 3, and 4 years. The results showed that the concrete mixed with Portland cement type I exhibited higher rate of the chloride penetration than the fly ash concrete. The chloride penetration of fly ash concrete was comparatively low and decreased with the increasing of fly ash content. The increase of fly ash replacement and the decrease of W/C ratio could reduce the covering depth required for the initial corrosion of the steel bar. Interestingly, fly ash concretes with 35% and 50% cement replacement and having W/C ratio of 0.65 provided better corrosion resistance at 4-year exposure than the control concrete with W/C ratio of 0.45. In addition, the covering depth of concrete with compressive strength of 30 MPa (W/C ratio of 0.65) could be reduced from 50 to 30 mm by the addition of fly ash up to 50%.     

Investigations about the influence of fine additives on the viscosity of cement paste for self-compacting concrete

In this work, the effect of fine additives (limestone, silica fume, fly ash, pozzolan, nano-silica fume) on the plastic viscosity of cement paste is being investigated. Towards this direction, twenty-four samples were designed and produced. Those pastes consisted mainly of cement (type CEM I 42.5) and specific proportions of one or two fine additives. Plastic viscosity and yield stress were measured, as well as micro-structure of selected 28-days hardened samples was studied through means of mercury porosimetry. Results showed that limestone (40%) can improve the rheological behavior of cement pastes, and the synergy of limestone (20%) and fly ash (20%) can lead to higher packing density. Cement pastes that combine those two characteristics, could serve as the base for self-compacting concrete (SCC) production.     

原状粉煤灰与钢纤维复合用于机场道面混凝土

将原状粉煤灰掺入机场道面用钢纤维混凝土中,研究了以原状粉煤灰等量取代、超量取代水泥及在水泥用量不变的条件下仅将其作为微细集料使用时对钢纤维混凝土性能的影响,探讨原状粉煤灰在机场道面用钢纤维混凝土中应用的可能性,以提高机场道面用钢纤维混凝土的力学性能,改善其内部结构,并降低一次性投资,为推广应用该项技术提供依据.     

掺活性掺合料的缓凝大流动性C80混凝土的性能研究

利用磨细矿渣粉、粉煤灰及二者复掺取代 30 %的水泥配制缓凝大流动性C80混凝土 ,测试了混凝土的力学性能以及干燥收缩、抗冻性、抗硫酸盐侵蚀性能、干热 -水浸泡循环作用下的性能等。研究表明 ,磨细矿渣粉单独掺入混凝土中仅有微弱的减水效应 ,但与高效减水剂共同使用时显示了显著的辅助减水效应。以掺合料与缓凝保塑高效减水剂共同配制的C80混凝土不仅流动性好 ,4h坍落度经时损失小 ,而且具有优异的力学性能 ,特别是掺磨细矿渣粉的混凝土早期力学性能与对比组接近。同时 ,掺磨细矿渣粉、粉煤灰或二者复掺的C80混凝土具有比对比混凝土更优越的抗干燥收缩性能、抗冻性、抗硫酸盐侵蚀性能及抗干热-水浸泡循环作用的性能     

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.     

粉煤灰对小砌块用混凝土性能的影响

研究了在小砌块用的混凝土中,以粉煤灰分别取代水泥和砂子及同时取代水泥和砂子对混凝土强度的影响,对低胶骨比混凝土中掺粉煤灰后,其强度提高、抗渗性能改善的机理进行了探索,通过工厂试生产表明：以生产ＭＵ７．５混凝土砌块的配合比为基准,掺１６％粉煤灰,砌块强度等级可提高到ＭＵ１０;抗渗性能从Ｑ级升为Ｓ级;节省水泥１５％,砂子４２％。     

矿物掺合料对干粉砂浆物理性能及孔结构的影响

研究了石灰石、矿渣和粉煤灰3种矿物掺合料分别对干粉砂浆的工作性能和力学性能的影响,并探讨了掺有掺合料时干粉砂浆的宏观力学性能和其微观孔结构之间的关系。结果表明:粉煤灰在掺量小于30%时能够提高砂浆的流动度,但掺量再继续增大时,砂浆流动度反而下降;掺入矿渣粉略能提高砂浆的流动度;石灰石粉在一定程度上降低砂浆流动度;同时石灰石粉能够提高砂浆的保水率,而矿渣粉和粉煤灰却降低砂浆的保水率。随着石灰石、矿渣和粉煤灰掺量的增加,砂浆28 d强度均有不同程度的降低,影响顺序为石灰石>粉煤灰>矿渣;与空白样相比,内掺占水泥质量50%的石灰石粉和矿渣粉时,28 d砂浆硬化体的总孔隙率分别增加10.2%、7.7%,而掺等量粉煤灰时总孔隙率则基本不变。以石灰石替代50%的水泥时,28 d砂浆硬化体中d>100 nm的多害孔增加24.0%,而以粉煤灰替代50%的水泥时,砂浆中多害孔基本不变,以等量的矿渣粉替代时d>100 nm的多害孔减少6.5%。     

Predicting the core compressive strength of self-compacting concrete (SCC) mixtures with mineral additives using artificial neural network

In this study, an artificial neural networks study was carried out to predict the core compressive strength of self-compacting concrete (SCC) mixtures with mineral additives. This study is based on the determination of the variation of core compressive strength, water absorption and unit weight in curtain wall elements. One conventional concrete (vibrated concrete) and six different self-compacting concrete (SCC) mixtures with mineral additives were prepared. SCC mixtures were produced as control concrete (without mineral additives), moreover fly ash and limestone powder were used with two different replacement ratios (15% and 30%) of cement and marble powder was used with 15% replacement ratio of cement. SCC mixtures were compared to conventional concrete according to the variation of compressive strength, water absorption and unit weight. It can be seen from this study, self-compacting concretes consolidated by its own weight homogeneously in the narrow reinforcement construction elements. Experimental results were also obtained by building models according to artificial neural network (ANN) to predict the core compressive strength. ANN model is constructed, trained and tested using these data. The results showed that ANN can be an alternative approach for the predicting the core compressive strength of self-compacting concrete (SCC) mixtures with mineral additives.     

Modeling of hydration kinetics in cement based materials considering the effects of curing temperature and applied pressure

Portland cement is the most widely used cement in the world. In the industrial by-products suitable for use as mineral admixtures in Portland concrete are ashes produced from the combustion of coal and granulated slag in metal industries. However, comparing such ashes with Portland cement, determining the hydration of this concrete is much more complex because of the reaction between calcium hydroxide and fly ash or slag. In this paper, the production of calcium hydroxide in cement hydration and its consumption in the reaction of mineral admixtures are considered in order to develop a numerical model for simulating the hydration of concrete, which contains fly ash or slag. The proposed numerical model includes the effects of water to binder ratios, slag or fly ash replacement ratios, curing temperature, and applied pressure. The heat evolution rate of fly ash- or slag-blended concrete is determined by the contribution of both cement hydration and the reaction of mineral admixtures. Furthermore, an adiabatic temperature rise in hardened blended concrete is evaluated based on the degree of hydration of the cement and mineral admixtures. The proposed model is verified through experimental data obtained from the concrete with different water-to-cement ratios and mineral admixture substitution ratios at elevated temperature and high pressure.