Transport and mechanical properties of self consolidating concrete with high volume fly ash

This paper presents the transport and mechanical properties of self consolidating concrete that contain high percentages of low-lime and high-lime fly ash (FA). Self consolidating concretes (SCC) containing five different contents of high-lime FA and low-lime FA as a replacement of cement (30, 40, 50, 60 and 70 by weight of total cementitious material) are examined. For comparison, a control SCC mixture without any FA was also produced. The fresh properties of the SCCs were observed through, slump flow time and diameter, V-funnel flow time, L-box height ratio, and segregation ratio. The hardened properties included the compressive strength, split tensile strength, drying shrinkage and transport properties (absorption, sorptivity and rapid chloride permeability tests) up to 365 days. Test results confirm that it is possible to produce SCC with a 70% of cement replacement by both types of FA. The use of high volumes of FA in SCC not only improved the workability and transport properties but also made it possible to produce concretes between 33 and 40 MPa compressive strength at 28 days, which exceeds the nominal compressive strength for normal concrete (30 MPa).     

Fresh properties of self-compacting cold bonded fly ash lightweight aggregate concrete with different mineral admixtures

This paper presents the results of an experimental study on the fresh properties of the self-compacting lightweight concretes made with cold bond fly ash (FA) lightweight aggregates. Binary and ternary use of FA and silica fume (SF) blends have been investigated in the production of self-compacting cold bonded FA lightweight aggregate concretes (SCLWCs). A total of 9 SCLWC mixtures were proportioned having constant water-binder ratio of 0.35 and the total binder content of 550?kg/m³. The control mixture contained only Portland cement (PC) as the binder while the remaining mixtures incorporated binary and ternary blends of PC, FA, and SF. After mixing, the fresh properties of the SCLWC were tested for T ₅₀₀ slump flow time, slump-flow diameter, V-funnel flow time and L-box height ratio. The fresh properties of SCLWCs with and without mineral admixtures were also evaluated by statistical technique, namely GLM-ANOVA. The results indicated that the combination use of FA and SF together decreased the slump flow time and V-funnel flow time. L-box height ratio, on the other hand, improved significantly.     

Filling ability and plastic settlement of self-compacting concrete

The use of self-compacting concrete (SCC) facilitates the placing of concrete by eliminating the need for compaction by vibration. Given the highly flowable nature of such concrete, care is required to ensure excellent filling ability and adequate stability. This is especially important in deep structural members and wall clements where concrete can block the flow, segregate and exhibit bleeding and settlement which can result in local defects that can reduce mechanical properties, durability and quality of surface finish.This paper shows results of an investigation of fresh properties of self-compacting concrete, such as filling ability measured by slump flow and flow time (measured by Orimet) and plastic fresh settlement measured in a columin. The SCC mixes incorporated various combinations of fine inorganic powders and admixtures. The slump flow of all SCCs was greater than 580 mm and the time in which the slumping concrete reached 500 mm was less than 3 s. The flow time was less than 5 s. The results on SCCs were compared to a control mix. The compressive strength and splitting tensile strength of SCCs were also measured.The effects of water/powder ratio, slump and nature of the sand on the fresh settlement were also evaluated. The volume of coarse aggregate and the dosage of superplasticizer were kept constant. It can be concluded that the settlement of fresh self-compacting concrete increased with the increase in water/powder ratio and slump. The nature of sand influenced the maximum settlement.     

Properties of self-compacting mortars with binary and ternary cementitious blends of fly ash and metakaolin

The link between flow properties and the formulation is actually one of the key-issues for the design of self-compacting concretes (SCC). As an integral part of a SCC, self-compacting mortars (SCMs) may serve as a basis for the design of concrete since the measurement of the rheological properties of SCCs is often impractical due to the need for complex equipment. This paper discusses the properties of SCMs with mineral admixtures. Portland cement (PC), metakaolin (MK), and fly ash (FA) were used in binary (two-component) and ternary (three-component) cementititios blends. Within the frame work of this experimental study, a total of 16 SCMs were prepared having a constant water-binder (w/b) ratio of 0.40 and total cementitious materials content of 550 kg/m³. Then, the fresh properties of the mortars were tested for mini-slump flow diameter, mini-V-funnel flow time, setting time, and viscosity. Moreover, development in the compressive strength and ultrasonic pulse velocity (UPV) of the hardened mortars were determined at 1, 3, 7, 14, and 28 days. Test results have shown that using of FA and MK in the ternary blends improved the fresh properties and rheology of the mixtures when compared to those containing binary blends of FA or MK.     

Effects of mineral admixtures on fresh and hardened properties of self-compacting concretes: binary,ternary and quaternary systems

The paper presented herein investigates the effects of using supplementary cementitious materials in binary, ternary, and quaternary blends on the fresh and hardened properties of self-compacting concretes (SCCs). A total of 22 concrete mixtures were designed having a constant water/binder ratio of 0.32 and total binder content of 550 kg/m³. The control mixture contained only 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 (GGBFS), and silica fume (SF). After mixing, the fresh properties of the concretes were tested for slump flow time, L-box height ratio, V-funnel flow time, setting time, and viscosity. Moreover, compressive strength, ultrasonic pulse velocity, and electrical resistivity of the hardened concretes were measured. Test results have revealed that incorporating the mineral admixtures improved the fresh properties and rheology of the concrete mixtures. The compressive strength and electrical resistivity of the concretes with SF and GGBFS were much higher than those of the control concrete.     

Properties of controlled low-strength materials incorporating cement kiln dust and slag

This research evaluated the potential use of cement kiln dust (CKD) together with slag to replace the use of cement in the production of controlled low-strength material (CLSM). The low strength requirements of CLSM compared to conventional concrete enable the use of industrial by-products for the production of CLSM. In this study, the workability-related fresh properties of CLSM mixtures were observed through slump flow diameter, V-funnel flow time and filling capacity. Setting times, temperature rise, air content and unit weight of CLSM mixtures were also determined as part of fresh properties. The hardened properties that were monitored for 28 days included the unconfined compressive strength. The test results presented herein show that a combination of less than 50 kg/m³ slag and up to 300 kg/m³ CKD provides a good mix that satisfies the requirements of a CLSM with similar or better properties to that of CKD-based CLSM mix containing Portland cement. Suitable CLSM mixtures with reasonable fresh and hardened properties could also be developed by using CKD alone. However, reduced strength in such CLSM mixtures may limit their field application. The slag significantly assisted in increasing compressive strength of CKD-based CLSM mixtures. A CLSM mix containing a combination of slag and CKD was shown to have excellent characteristics for flowable backfill and excavatable base material. Therefore, producing CKD/slag based CLSM through the use of co-generated products from the cement and iron manufacturing processes can provide leadership for the construction industry in the transition for sustainable development.     

Properties of self-compacting concrete prepared with coarse and fine recycled concrete aggregates

In this study, the fresh and hardened properties of self-compacting concrete (SCC) using recycled concrete aggregate as both coarse and fine aggregates were evaluated. Three series of SCC mixtures were prepared with 100% coarse recycled aggregates, and different levels of fine recycled aggregates were used to replace river sand. The cement content was kept constant for all concrete mixtures. The SCC mixtures were prepared with 0, 25, 50, 75 and 100% fine recycled aggregates, the corresponding water-to-binder ratios (W/B) were 0.53 and 0.44 for the SCC mixtures in Series I and II, respectively. The SCC mixtures in Series III were prepared with 100% recycled concrete aggregates (both coarse and fine) but three different W/B ratios of 0.44, 0.40 and 0.35 were used. Different tests covering fresh, hardened and durability properties of these SCC mixtures were executed. The results indicate that the properties of the SCCs made from river sand and crushed fine recycled aggregates showed only slight differences. The feasibility of utilizing fine and coarse recycled aggregates with rejected fly ash and Class F fly ash for self-compacting concrete has been demonstrated.     

Properties of self-compacting portland pozzolana and limestone blended cement concretes containing different replacement levels of slag

In order to reduce energy consumption and CO₂ emission, and increase production, cement manufacturers are blending or inter-grinding mineral additives such as slag, natural pozzolana, and limestone. This paper reports on the results of an experimental study on the production of self-compacting concrete (SCC) produced with portland cement (PC), portland pozzolana (PPC) and portland limestone (PLC) blended cements. Moreover, the effect of different replacement levels (0–45%) of ground granulated blast furnace slag (GGBFS) with the PPC, PLC, and PC cements on fresh properties (such as slump flow diameter, T ₅₀₀ slump flow time, V-funnel flow time, L-box height ratio, setting time, and viscosity) and hardened properties (such as compressive strength and ultrasonic pulse velocity) of self-compacting concretes are investigated. From the test results, it was found that it was possible to manufacture self-compacting concretes with PPC or PLC cements with comparable or superior performance to that of PC cement. Furthermore, the use of GGBFS in plain and especially blended cement self-compacting concrete production considerably enhanced the fresh characteristics of SCCs.     

Influence of cement type on ITZ porosity and chloride resistance of self-compacting concrete

With the increasing use of self-compacting concrete (SCC) its durability has come into focus. Concerning the microstructure of concrete, the porosity in the interfacial transition zone (ITZ) is regarded as a key feature for permeability and durability. Generally, a combination of cement and mineral admixtures is used for the production of SCC. In the present study, ITZ porosity of four SCC mixtures produced with ordinary Portland cement, Portland limestone cement, slag cement and ordinary Portland cement combined with fly ash is analyzed. Additionally, the chloride migration coefficient is determined. ITZ porosity and width of the SCC mixtures are similar. The substantial differences in the chloride migration coefficients show that the binder type has a stronger influence on permeability than the pore volume in the ITZ.     

Effects of granulated blast furnace slag and superplasticizer type on the fresh properties and compressive strength of self-compacting concrete

This paper presents the results of an experimental investigation carried out to study the effect of granulated blast furnace slag and two types of superplasticizers on the properties of self-compacting concrete (SCC). In control SCC, cement was replaced with 10%, 15%, 20%, and 25% of blast furnace slag. Two types of superplasticizers: polycarboxylate based superplasticizer and naphthalene sulphonate based superplasticizers were used. Tests were conducted for slump flow, the modified slump test, V-Funnel, J-Ring, U-Box, and compressive strength. The results showed that polycarboxylate based superplasticizer concrete mixes give more workability and higher compressive strength, at all ages, than those with naphthalene sulphonate based superplasticizer. Inclusion of blast furnace slag by substitution to cement was found to be very beneficial to fresh self-compacting concrete. An improvement of workability was observed up to 20% of slag content with an optimum content of 15%. Workability retention of about 45 min with 15% and 20% of slag content was obtained using a polycarboxylate based superplasticizer; compressive strength decreased with the increase in slag content, as occurs for vibrated concrete, although at later ages the differences were small.     

Properties of self-compacting concrete prepared with recycled glass aggregate

The effects of recycled glass (RG) cullet on fresh and hardened properties of self-compacting concrete (SCC) were investigated. RG was used to replace river sand (in proportions of 10%, 20% and 30%), and 10 mm granite (5%, 10% and 15%) in making the SCC concrete mixes. Fly ash was used in the concrete mixes to suppress the potential alkali-silica reaction. The experimental results showed that the slump flow, blocking ratio, air content of the RG–SCC mixes increased with increasing recycled glass content. The compressive strength, tensile splitting strength and static modulus of elasticity of the RG–SCC mixes were decreased with an increase in recycled glass aggregate content. Moreover, the resistance to chloride ion penetration increased and the drying shrinkage of the RG–SCC mixes decreased when the recycled glass content increased. The results showed that it is feasible to produce SCC with recycled glass cullet.     

Mechanical and durability performance of sustainable structural concretes: An experimental study

This study reports the results of a wide experimental campaign intended at investigating the mechanical and durability performance of structural concretes made with Recycled Concrete Aggregates (RCAs) and coal Fly Ash (FA). To this end, twelve mixtures were designed by replacing part of the ordinary constituents (i.e. cement, sand and coarse aggregates) of a reference one with RCAs and FA. Samples of these mixtures were subjected to various tests aimed at assessing both their structural properties and durability performance. As for the former, time evolution of compressive strength was monitored at various curing times up to 365 days, and the splitting strength was determined at 28 days. Moreover, the expected durability performance of the aforementioned concrete mixtures was scrutinised by measuring some relevant physical quantities, such as water permeability, carbonation depth and chloride-ions ingress at various curing ages.The results obtained from these tests are often not self-evident, as they unveil the synergistic effect of combining both RCAs and FA on the resulting physical and mechanical properties of “green” concrete. Moreover, they demonstrate that the current code restrictions on the use of both RCAs and FA for structural concrete might be significantly relaxed, especially if the delayed binder effect, induced by the latter, is duly taken into account and, hence, concrete properties are measured at curing times longer than the conventional 28 days.     

Mechanical properties of prestressed self-consolidating concrete

Since the mix design of self-consolidating concrete (SCC) differs from that of conventional concrete, mechanical properties of SCC may differ from those of vibrated concrete. An experimental program was performed to evaluate mechanical properties of SCC used for precast, prestressed applications. Sixteen SCC mixtures with a fixed slump flow of 680 ± 20 mm were prepared with different mixture parameters, including binder content and binder type, w/cm, dosage of viscosity-modifying admixture, and sand-to-total aggregate volume ratio. Two high-performance concrete mixtures that represent typically concrete used for precast, prestressed applications were investigated for the control mixtures. They were proportioned with 0.34 and 0.38 w/cm and had slump values of 150 mm. Mechanical properties of SCC were compared to code provisions to estimate compressive strength, elastic modulus, and flexural strength. The modified ACI 209-90 and CEB-FIP MC90 codes are found to provide good estimate for compressive strength prediction. The AASHTO 2007 model can provide good prediction of the elastic modulus and flexural strength of SCC.     

Durability characteristics of self-consolidating concrete designated for repair applications

This paper presents test results carried out to study the influence of key mixture parameters on frost durability, scaling resistance, and transport properties of self-consolidating concrete (SCC) that can be used in structural repair. Regardless of the w/cm, binder type, or admixture combination, properly designed SCC can develop high resistance to freezing and thawing with frost durability factor greater than 80%. The optimized mixtures had 56-day rapid chloride-ion permeability (RCP) values of 200–900 Coulomb. On the average, SCC made with 0.42 w/cm developed 20% higher capillary porosity, 20% lower compressive strength, and 30% greater RCP value compared to similar SCC prepared with 0.35 w/cm. The type of blended cement in use had considerable influence on transport properties. For a given mix design, concrete with 180 mm slump consistency exhibited similar RCP value of 505 Coulomb compared to 630 Coulomb for the same concrete with greater dosage of HRWRA to secure a slump flow consistency of 670 mm.     

Durability performance potential and strength of blended Portland limestone cement concrete

This paper describes a study on the durability potential and strength of composite Portland-limestone cement (PLC) concrete mixtures blended with ground granulated blast furnace slag (GGBS) and/or fly ash (FA). Their performance was compared against ordinary Portland cement, plain PLC and Portland-slag cement concrete mixtures. Using the South African Durability Index approach, results indicate reductions in the penetrability of the composite PLC blends compared to the other mixtures. The durability indicators are chloride conductivity, gas (oxygen) permeability and water sorptivity. Compressive strength of the composite PLC mixtures containing both GGBS and FA showed competitive performance with the comparative mixtures, but FA blended PLC mixtures had diminished compressive strength values. The paper also presents considerations on the practical implications of using blended PLC concrete mixtures.     

The behaviour of concrete in hot climates

The paper, after very briefly discussing the classification of world climates, considers hot climates before taking up a review of papers dealing with the effects of hot climates on the properties of both fresh and hardened concrete. Raw materials for concrete are discussed, where the adverse and positive effects of C₃A and gypsum contents of Portland cement, thermal movement of concrete and sulphate and chloride contents of aggregate and mixing water in hot climates are pointed out. The effect of elevated temperature, ambient and initial paste temperature, ambient relative humidity, solar radiation, and water/cement ratio on the rate of Portland cement hydration and hydration product structure are discussed. The behaviours of both fresh and hardened concrete are taken up. The effect of evaporation from a fresh concrete surface on the behaviour of hardened concrete is discussed. The paper concludes that the presently published works on the properties of concrete in hot climates are fragmentary, uncoordinated and at times contradictory. It points out that systematic studies of the properties of concrete cast and continuously exposed to either hot-humid or hot-dry climates remain to be done.     

Utilization of ceramic waste as fine aggregate within Portland cement and fly ash concretes

The aim of this research work was to investigate the feasibility of using ceramic waste and fly ash to produce mortar and concrete. Ceramic waste fragments obtained from local industry were crushed and sieved to produce fine aggregates. The measured concrete properties demonstrate that while workability was reduced with increasing ceramic waste content for Portland cement concrete and fly ash concrete, the workability of the fly ash concrete with 100% ceramic waste as fine aggregate remained sufficient, in contrast to the Portland cement control concrete with 100% ceramic waste where close to zero slump was measured. The compressive strength of ceramic waste concrete was found to increase with ceramic waste content and was optimum at 50% for the control concrete, dropping when the ceramic waste content was increased beyond 50%. This was a direct consequence of having a less workable concrete. However, the compressive strength in the fly ash concrete increased with increasing ceramic waste content up to 100%. The benefits of using ceramic waste as fine aggregate in concrete containing fly ash were therefore verified.     

Effect of the use of different types and dosages of mineral additions on the bond strength of lap-spliced bars in self-compacting concrete

In this study, nine different types of concrete were adopted: normal concrete (NC) with low slump (68 mm) and eight types of self-compacting concrete (SCC) in which cement was partially replaced by four kinds of replacements (25%, 30%, 35% and 40%) of class F fly ash (FA) and by four kinds of replacements (5%, 10%, 15% and 20%) of silica fume (SF). The main objective of this research was to evaluate the effect of different types and dosages of mineral additions on the moment capacities and stiffnesses of the beam specimens and the bond strength of tension lap-spliced bars embedded in NC and self-compacting concretes (SCCs). To achieve these objectives, 27 full-scale beam specimens (2000 × 300 × 200 mm) were tested. In all beam specimens, 20 mm reinforcing bars were used with a 300 mm splice length as tension reinforcement. The variable used was the amount of FA and SF incorporated into SCC. Each beam was designed with bars spliced in a constant moment region at midspan. The splice length was selected so that bars would fail in bond, splitting the concrete cover in the splice region, before reaching the yield point. Moreover, bond strength of SCC beams was compared to that of NC beams of the same dimensions, steel configuration and approximately the same water-to-cement ratio. In conclusion, the beam specimens produced from SCC containing 5% SF and 30% FA had the highest normalized bond strength with 1.07 whilst the replacements of Portland cement (PC) by an equal weight of FA or SF in SCC had generally the positive effect on the bond strength of reinforcing bar regardless of the dosage of mineral admixture compared to the specimen with NC indicating that SCC due to its superior filling capability more effectively covered the reinforcements and the grain-size distribution and particle packing improved ensuring greater cohesiveness. Moreover, the beam specimens produced from SCC with SF had the greatest stiffness compared to other all beams as result of the improvement of concrete pore structure due to the pozzolanic activity and the filler effect of high fineness silica fume.     

Comparison of in situ properties of wall elements cast using self-consolidating concrete

An experimental program was undertaken to investigate the homogeneity of in situ properties of wall elements cast with various commercially available self-consolidating concrete (SCC) mixtures. Wall elements measuring 5?m in length, 1.6?m in height, and 0.35?m in width were cast. The SCC mixtures were proportioned with various binders and admixtures and had different levels of slump flow consistency and design compressive strengths. The SCC mixtures exhibited adequate passing ability with L-box blocking ratio higher than 0.70 and filling capacity greater than 80%. All cast walls exhibited homogeneous in situ mechanical properties, regardless of the core location. The coefficient of variation (COV) of in situ compressive strength values ranged from 3 to 6%. Conventional vibrated concrete used to cast a reference wall element led to relatively large spread in in situ rapid chloride-ion permeability values and high COV of spacing factor compared to those of the various SCC wall elements (17% vs. 6?C12%). Good correlation was established between surface settlement and top-bar factor of reinforcing bars embedded along the various heights of the 1.6-m high walls. On average, concrete with 0.50% surface settlement was shown to exhibit a maximum top-bar factor of 1.4. The mean top-bar factor values near the top of walls cast with SCC were limited to 1.4, which is considered a low value given the high slump flow of the concrete and the depth of cast elements.