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.     

Effect of admixtures on the setting times of high-strength concrete

The effect of silica fume (SF), metakaolin (MK), fly ash (FA) and ground granulated blast-furnace slag (GGBS) on the setting times of high-strength concrete has been investigated using the penetration resistance method (ASTM C 403). In addition, the effect of a shrinkage-reducing admixture (SRA) on the setting times of normal and high-strength concrete was also studied. The setting times of the high-strength concrete were generally retarded when the mineral admixtures replaced part of the cement. While the SRA was found to have negligible effect on the setting times of normal strength concrete, it exhibited a rather significant retarding effect when used in combination with superplasticiser in high-strength concrete. The inclusion of GGBS at replacement levels of 40% and greater resulted in significant retardation in setting times. In general, as replacement levels of the mineral admixtures were increased, there was greater retardation in setting times. However, for the concrete containing MK, this was only observed up to a replacement level of 10%.     

Performance of metakaolin concrete at elevated temperatures

An experimental investigation was conducted to evaluate the performance of metakaolin (MK) concrete at elevated temperatures up to 800 °C. Eight normal and high strength concrete (HSC) mixes incorporating 0%, 5%, 10% and 20% MK were prepared. The residual compressive strength, chloride-ion penetration, porosity and average pore sizes were measured and compared with silica fume (SF), fly ash (FA) and pure ordinary Portland cement (OPC) concretes. It was found that after an increase in compressive strength at 200 °C, the MK concrete suffered a more severe loss of compressive strength and permeability-related durability than the corresponding SF, FA and OPC concretes at higher temperatures. Explosive spalling was observed in both normal and high strength MK concretes and the frequency increased with higher MK contents.     

Optimization of rheological properties of oil well cement slurries using experimental design

This paper proposes a statistical design approach based on a second order central composite response surface model to predict the rheological properties of oil well cement (OWC) slurries incorporating metakaolin (MK), silica fume (SF), rice husk ask (RHA) or fly ash (FA). The proposed models are for OWC partial replacement levels ranging from 5 to 15% by MK, SF, RHA or FA used along with a new generation polycarboxylate-based high-range water reducing admixture (PCH) at dosages ranging from 0.25 to 1.5% and at different temperatures ranging from 23 to 60°C. The significance and validity of the models were confirmed by statistical analysis and verification experiments. The regression models were used to analyze the influence of the mixture proportion as well as temperature on the rheological properties of OWC slurries. The statistical design can be applied to optimize rheological properties such as yield stress and plastic viscosity considering the addition of supplementary cementitious materials (SCMs) at different temperatures, and to gain a better understanding of trade-offs between key mixture parameters such as the superplasticizer dosage and the level of SCMs used.     

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.     

The influence of supplementary cementing materials on water retaining characteristics of hydrated lime and cement mortars in masonry construction

The purpose of this paper is an investigation of the possible role of supplementary cementing materials (SCMs) on the water retaining ability of hydrated lime (CL90) and Portland cement (PC) mortars. Desorptivity (R) defines the water retaining ability of mortars in the freshly-mixed wet state. Transfer sorptivity (A) defines the ability of the substrate to withdraw water from the wet mix. The time to dewater (t _dw), is an expression derived from the sharp front theory, and enables calculation of the time taken for a wet mortar joint to be dewatered by an absorbent substrate. The results show that the very water retaining CL90 mortars become progressively more water releasing with increased volume fraction replacement levels of both ground granulated blast-furnace slag (GGBS) and fly ash (FA). On the other hand, the very water releasing PC mortars become more water retaining with the addition of silica fume (SF). Results also show that transfer sorptivity increases as the volume fraction replacement levels of GGBS and FA increases in CL90 mortars and decreases with increased volume fraction replacement levels of SF in PC mortars. Since the time taken to dewater a mortar joint (t _dw) is inversely proportional to the squared transfer sorptivity, t _dw can be dramatically altered by the addition of SCMs in both CL90 and PC mortars. These parameters have important practical consequences, not only in the initial adhesion of the mortar to the substrate but also in the strength of the set material. The ability to manipulate the water retaining properties can also allow construction time to be reduced.     

Durability aspect of concretes composed of cold bonded and sintered fly ash lightweight aggregates

This study reports the finding of an experimental study carried out on the durability related properties of the lightweight concretes (LWCs) including either cold bonded (CB) or sintered (S) fly ash aggregates. CB aggregate was produced with cold bonding pelletization of class F fly ash (FA) and Portland cement (PC) while S aggregate was produced by sintering the fresh aggregate pellets manufactured from FA and bentonite (BN). Two concrete series with water-to-binder (w/b) ratios of 0.35 and 0.55 were designed. Moreover, silica fume (SF) with 10% replacement level was also utilized for the purpose of comparing the performances of LWCs with and without ultrafine SF. The durability properties of concretes composed of CB and S aggregates were evaluated in terms of water sorptivity, rapid chloride ion permeability, gas permeability, and accelerated corrosion testing after 28 days of water curing period. The compressive strength test was also applied to observe the strength level at the same age. The results revealed that S aggregate containing LWCs had relatively better performance than LWCs with CB aggregates. Moreover, the incorporation of SF provided further enhancement in permeability and corrosion resistance of the concretes.     

Effect of volcanic pumice powder on the fresh properties of self-compacting concretes with and without silica fume

The current study presents an experimental study conducted on the effectiveness of volcanic pumice powder (VP) on the fresh properties of self-compacting concretes (SCCs) with and without silica fume (SF). In the first group, SCCs without SF were produced with 0, 5, 10, and 20 % replacement levels of VP. However, for the second group, SF incorporation was achieved by a constant SF replacement level of 8 %. All of the replacement levels assigned were substitution of cement with the supplementary cementing materials on the basis of weight of total binder. Therefore, totally eight different SCCs were produced. The investigated fresh characteristics of the concretes were slump flow diameter, T _500mm slump flow time, V-funnel flow time, and L-box height ratio. The compressive strength of concretes was also evaluated to indicate the mechanical performance. Moreover, a statistical study, namely general linear model analysis of variance, was performed in order to examine the significance of the critical parameters such as inclusion of SF and replacement level of VP on the properties of SCCs. The results have revealed that increasing the replacement level of VP generally resulted in the increase of fluidity of SCCs without loss of uniformity and with no segregation. Moreover, incorporation of SF provided significant increase in compressive strength while VP caused a systematic decrease.     

Influence of steam curing on the properties of concretes incorporating metakaolin and silica fume

In this paper, influence of steam curing on the compressive strength, ultrasonic pulse velocity, water sorptivity, chloride ion permeability, and electrical resistivity of metakaolin and silica fume blended concretes were investigated. A total of seven mixtures containing various combinations of Portland cement (PC), silica fume (SF), and metakaolin (MK) were produced with 400 kg/m³ of total cementitious materials content and with a constant water/binder ratio of 0.44. For each mixture, concrete samples were either standard-cured in water at 23°C or steam-cured at 70°C maximum temperature over 17 h curing period. Test results revealed that steam curing enhanced the 1-day compressive strength and ultrasonic pulse velocity while leading to reduced long term strength in line with earlier findings. At the end of the water sorptivity, chloride ion permeability, and electrical resistivity tests, it was found that the steam-cured concretes had higher water sorptivity and chloride ion permeability, and lower electrical resistivity values compared to the standard cured specimens. Use of SF and MK as cementitious materials remarkably decreased the water sorptivity and chloride ion permeability of concretes, irrespective of the curing condition.     

The effect of limestone powder,fly ash and silica fume on the properties of self-compacting repair mortars

Self-compacting repair mortars (SCRM) are preferred for the rehabilitation and repair of reinforced concrete structures especially at narrow mould systems. Self compactability and stability are susceptible to ternary effects of chemical and mineral admixture type and their content. In this study, the effect of limestone powder (LP) on the properties of SCRM has been compared with other mineral additives (silica fume (SF) and fly ash (FA) and their combinations) effects. Fresh properties, flexural and compressive strengths and water absorption properties of mortars were determined. The use of SF in mortars significantly increased the dosage of superplasticiser (SP). At the same constant SP dosage (0·8%) and mineral additives content (30%), LP can better improve the workability than that of control and FA mixtures by 19% and 27%. However, the results of this study suggest that certain FA, SF and LP combinations can improve the workability of SCRMs, more than FA, SF and LP alone. LP can have a positive influence on the mechanical performance at early strength development while SF improved aggregate-matrix bond resulting from the formation of a less porous transition zone in mortar. SF can better reducing effect on total water absorption while FA and LP will not have the same effect, at 28 days.     

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.     

Mechanical strength and setting times estimation of hydroxyapatite cement by using neural network

In this study, the mechanical strength, the initial and the final setting times in hydroxyapatite (HA) bone cement are estimated by designing a back-propagation neural network (BPNN) which has 2 inputs and 3 outputs. Firstly, some experimental samples have been prepared to train the BPNN to get it to estimate the output parameters. Then BPNN is tested using some experimental samples that have not been used in the training stage. To prepare the training and testing data sets, some experiments were performed. In these experiments, the β-tricalcium phosphate (β-TCP), the calcium carbonate and the dicalcium phosphate are used to prepare the powder part of the HA bone cement. Also the liquid part of the cement consists of the NaH₂PO₄⋅2H₂O solution with different concentrations. The effects of liquid phase concentration and the liquid/powder ratio of the cement, as input parameters, have been investigated on the setting times and the mechanical strength of the cement, as output parameters. The comparison of the predicted values and the experimental data indicates that the developed model has an acceptable performance to estimation of the setting times and the mechanical strength in HA bone cement. Also three neural networks with 2-inputs and 1-output was developed, similar to above method, and were compared with 3-outputs model. It is found that the prediction accuracy of 3-outputs model is better than those of other 1-output models.     

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.     

Optimization of concrete mixture with hybrid blends of metakaolin and fly ash using response surface method

This paper presents the experimental results of a research carried out on the strength and permeability related properties of high performance concretes made with binary and ternary cementitious blends of fly ash (FA) and metakaolin (MK). The replacement ratios for FA were 10% and 20% by weight of Portland cement and those for MK were 5% and 10%. Compressive strength, chloride permeability, water sorptivity, and water absorption properties of concretes were obtained in this study for different testing ages up to 90 days. The influences of fly ash, metakaolin, and testing age on the properties of concretes have been identified using the analysis of variance. The statistical based regression models and the response surface method with the backward stepwise techniques were employed in the multi-objective optimization analysis. That is carried out by maximizing compressive strength while minimizing chloride permeability, water sorptivity, and water absorption. It was observed that fly ash and especially metakaolin were very effective on the aforementioned properties of the concretes, depending mainly on replacement levels and duration of curing. The results indicated that the ternary use of fly ash and metakaolin with the approximate cement replacement values of 13.3% and 10% respectively has provided the best results for the testing age of 90 days, when the optimized strength and permeability based durability properties of the concretes are concerned.     

Effects of different curing regimes on the compressive strength properties of self compacting concrete incorporating fly ash and silica fume

This paper presents the effect of air curing, water curing and steam curing on the compressive strength of Self Compacting Concrete (SCC). For experimental study, SCC is produced with using silica fume (SF) instead of cement by weight, by the ratios of 5%, 10% and 15%, and fly ash (FA) with the ratios of 25%, 40% and 55%. It is observed that mineral admixtures have positive effects on the self settlement properties. The highest compressive strength was observed in the concrete specimens with using 15% SF and for 28 days water curing. Air curing caused compressive strength losses in all groups. Relative strengths of concretes with mineral admixtures were determined higher than concretes without admixtures at steam curing conditions.     

Investigation into the synergistic effects in ternary cementitious systems containing portland cement, fly ash and silica fume

This research was primarily conducted to verify the presence of synergistic effects in ternary cementitious systems containing portland cement (OPC), class C fly ash (FA) and silica fume (SF). A subsequent objective of the study was to quantify the magnitude of the synergy and to determine its source. For a ternary mixture containing 20% FA and 5% SF by mass, the synergistic effect was observed mostly at later ages (7 days onward) and it resulted in an increased compressive strength and resistance to chloride ion penetration as well as a reduced rate of water absorption (sorptivity) compared to predictions based on individual effects of FA and SF in respective binary systems. The observed synergy was attributed to both chemical and physical effects. The chemical effect manifested itself in the form of an increased amount of hydration products. The physical effect associated with packing density was, somewhat contrary to general belief, not due to an optimized particle size distribution of the binder components of the ternary cementitious system. Instead, it was the result of smaller initial inter-particle spacing caused by lower specific gravities of both FA and SF which, in turn, led to a lower volumetric w/cm. If the mixture design was adjusted to account for these differences, the physical effect would be diminished.     

Effects of marble powder and slag on the properties of self compacting mortars

In this study, binary and ternary use of marble powder (MP) and ground granulated blast furnace slag (GGBFS) have been investigated in the production of self compacting mortars (SCMs). The marble powder was obtained as an industrial by-product during sawing, shaping, and polishing of marble. A total of 19 SCM mixtures were proportioned having a constant water-binder ratio of 0.40 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, MP, and GGBFS. After mixing, the fresh properties of the SCM were tested for mini-slump flow diameter, mini-V funnel flow time, initial and final setting times, and viscosity. Moreover, compressive strength and ultrasonic pulse velocity of the hardened SCMs were measured. Test results indicated that the inclusion of MP increased the V-funnel flow time, setting times, and viscosity of SCMs whereas decreased the hardened properties. Using GGBFS, on the other hand, decreased the V-funnel flow time and viscosity while increased the setting times of SCMs.     

Effect of pozzolans on the performance of fiber-reinforced mortars

Randomly oriented short fibers have been shown to increase tensile strength and retard crack propagation of cement based materials such as fiber-reinforced mortars for diverse applications, especially in aggressive environments. In the case of reinforced concrete, it is very important to produce a “high quality” cover in order to prevent corrosion of the rebars. In order to obtain a high performance material the use of a pozzolan is advisable because low permeability is achieved. The objective of this research was to determine the effect of pozzolans such as silica fume (SF), fly ash (FA), and metakaolin (MK) on the properties of fiber-reinforced mortars. Different types of natural and synthetic fibers were used. A superplasticizer was used to keep the same workability as that of the control mortar. Results of the mechanical and durability properties of the fiber-reinforced mortars are reported. The results show that a loss of resistance due to embedding fibers in mortar is compensated for by the increase in strength caused by silica fume or metakaolin additions to the mortar. The addition of 15% of SF or MK produces an improvement of up to 20% and 68%, respectively, when compared with those mortars without addition. There is a significant decrease in the coefficient of capillary absorption and chloride penetration when a highly pozzolanic material is incorporated into the matrix. In general, these materials, especially SF and MK, improve the mechanical performance and the durability of fiber-reinforced materials, especially those reinforced with steel, glass or sisal fibers. The fly ash addition had a different performance, which could be attributed to its low degree of pozzolanicity.     

Effect of metakaolin and silica fume on the durability of self-consolidating concrete

Metakaolin (MK) is a valuable admixture for concrete/cement applications that can enhance the performance of cementitious composites through high pozzolanic reactivity, much like silica fume (SF). While SF concrete is characterized by superior mechanical and durability performance, concrete containing MK achieves comparable properties at a lower price and with better workability. The objective of this study is to investigate the effect of cement replacement by MK on the durability of self-consolidating concrete (SCC); the effect of SF at similar levels of MK replacement has also been included for comparison. The durability performance of SCC was evaluated based on the results of drying shrinkage, freezing and thawing, salt scaling, and rapid chloride permeability tests. The results of these tests indicate that highly durable SCC mixtures can be produced using a high MK content with an optimum percentage of around 20%. The results also show that the durability of SCC, especially with high MK content, is higher than that of SCC containing SF.