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 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.     

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.     

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).     

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.     

Development of microfine cement grouts by pulverizing ordinary cements

Three different cements (CEM I, CEM II/B-M and CEM IV/B according to EN 197-1) containing 0%, 23.5% and 38% of pozzolan, respectively, were pulverized to obtain three additional gradations from each cement, with nominal maximum grain sizes of 40, 20 and 10 μm. Cements with the two finer gradations are classified as “microfine” cements. Suspension properties, groutability and effectiveness of all cements were evaluated for water-to-cement ratios (W/C) of 1, 2 and 3 by weight. A superplasticizer was used to optimize rheological properties. The properties and performance of all suspensions tested are affected primarily by W/C ratio and cement fineness. All microfine cement suspensions have acceptable apparent viscosity, behave as Bingham fluids, are stable for W/C = 1, have reasonable setting times for field applications, have mostly predictable groutability and provide satisfactory strength to grouted sands. The finer gradations of II/B-M cement exhibited the best overall behavior and are considered as the most promising compared to similar gradations of the other two cements.     

Impact of powder composition on processing-relevant properties of pharmaceutical materials: An experimental study

In this work, we studied the influence of powder composition on packing density and other processing-relevant properties of binary mixtures, including powder flowability. Binary mixtures of pharmaceutical powders with different particle size ratios, α and varying fractions of large and small particles were analyzed systematically. Mixtures of three excipients and one API with different composition (2, 5, 10, 30, 50, 70, 90, 95 and 98 wt%) were prepared in a Turbula mixer. Powders with different properties and particle size distribution were chosen, in order to obtain three binary mixtures with different size ratios. Then, macroscopic powder properties including bulk (poured) and tapped density (BD and TD) were measured. A powder rheometer was used to measure the flow function coefficient (ffc), cohesion, compressibility and permeability of the binary mixtures. We considered experimentally three classes of binary mixtures, which are characterized by two critical ratios of particle diameter: the critical size ratio of entrance (α_c) and the critical size ratio of replacement (α_r), where α_c = 0.154 and α_r = 0.741. Below the critical size ratio of entrance (α_c), the particle asymmetry (ratio between large and small particle diameters) is high and small particles can fill the voids between larger ones. Between α_c and the critical size ratio of replacement (α_r), the smaller particles are too large to fit in the voids between larger particles (packing structure changes). Above α_r, the particles are more or less symmetric in size and overall packing structure does not change by mixing the particles. Our experiments show that there is a non-linear and non-monotonic dependence of all relevant properties on composition for powder mixtures that have an α < α_r. This non-linear behavior is even more significant for strongly asymmetric binary mixtures with α < α_c. We argue that this behavior is related to the composition dependence of random packing of particulate systems. Our results have relevance to pharmaceutical particle processing operations where constant powder mixture properties are needed to ensure quality standards are met; such operations include capsule or die filling during tableting, and the continuous feeding of powders via screw feeders. Our results suggest that for pharmaceutical particle processing operations, where constant powder mixture properties are a prerequisite for process robustness, the size ratio of API and excipient particles, α should not be smaller than α_r = 0.741.     

Unloading‐Based Stiffness Characterisation of Cement Pastes During the Second,Third and Fourth Day After Production

The stiffness evolution of binder ‘cement paste’ is triggering the stiffness of concrete. In the engineering practice, concrete formworks are typically removed 24 h after production. This underlines that knowledge on mechanical properties of cementitious materials during the second, third and fourth day after production is of high relevance for the ongoing construction process. This provides the motivation to perform early‐age stiffness characterisation on hydrating cement pastes, by means of the following three test methods. Unloading modulus is determined using a novel setup for non‐destructive uniaxial compression testing including overdetermined deformation measurements. Dynamic Young's moduli are obtained from ultrasonics experiments. Isothermal differential calorimetry allows for linking the observed temporal evolution of early‐age stiffness to the hydration degree of cement. Pastes with three different compositions are investigated, defined in terms of the initial water‐to‐cement mass ratio w/c and the initial water‐to‐solid (binder) mass ratio w/s. Pure cement pastes exhibit w/c = w/s = 0.50 and w/c = w/s = 0.42, respectively. A fly ash‐blended cement paste refers to a cement mass replacement level of 16%, and this is related to w/c = 0.50 and w/s = 0.42. Both unloading moduli and dynamic Young's moduli of all three materials increase practically linearly with increasing hydration degree, in the investigated regime of hydration degrees ranging from 40 to 60%. Fly ash does not contribute significantly to the early‐age hydration of the material, i.e. it represents a quasi‐inert part of the material's microstructure, exhibiting a significant stiffening effect.     

Effect of temperature on the rheology of flowable mortars

In addition to the characteristics of mixture constituents and mix design, the rheological behavior of concrete is influenced by material temperature and time after water–cement contact. The study presented herein evaluates the combined influence of time and temperature on the workability of micro mortars. The mixtures were proportioned with polymelamine (PMS), polynaphtalene (PNS), polycarboxylate (PCP) polymer, and made of different supplementary cementitious materials. Seven micro mortars proportioned with various binder compositions and water-to-binder ratio of 0.42 and 0.53 were prepared at 10–33 °C. Test results show that the yield stress and plastic viscosity vary linearly with the coupled effect of time and temperature for mixtures made with PNS or PMS superplasticizers. However, for mixtures made with PCP superplasticizer, both the material temperature and type of supplementary cementitious materials are shown to influence the evolution of rheology with time.     

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.     

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.     

Numerical simulation of self-consolidating concrete flow as a heterogeneous material in L-Box set-up: Effect of rheological parameters on flow performance

A computational fluid dynamics (CFD) software was used to simulate the effect of rheological parameters on the heterogeneous performance properties of self-consolidating concrete (SCC) in the horizontal and vertical directions of the L-Box set-up. These properties consist of flowability, blocking resistance, and dynamic segregation. Different suspending fluids having five plastic viscosity values (10–50 Pa.s), three yield stress values (14–75 Pa), two fluid densities (2000 and 2500 kg/m³), and two shear elasticity modulus values (100 and 1000 Pa) were considered. The suspensions consisted of a number of 135 in total spherical particles with 20-mm in diameter and 2500 kg/m³ density.The results of 25 simulations in total are found to correlate well with the rheological parameters of the suspending fluid. Plastic viscosity of the suspending fluid was shown to be the most dominant parameter affecting flow performance of SCC in the L-Box test. A new approach was also proposed to classify SCC mixtures based on the filling ability properties.     

Processing of concentrated aqueous fluorapatite suspensions by slip casting

In order to produce stable aqueous fluorapatite (FA) suspensions, its surface reactivity in an aqueous solution having two initial pH values with a concentration of ammonium polyacrylate (NH₄PA) was investigated as a function of time. The rheological behaviour of concentrated aqueous FA slips stabilized with NH₄PA was studied; besides, the effect of poly(vinyl)alcohol (PVA) addition on the relative viscosity of the suspensions was investigated. The influence of the slip rheology on the microstructure of the resultant green slip cast compacts and their sintering behaviour were determined. Upon the FA introduction in the aqueous solutions, an initial release of F anions located at the surface was found, which was not dependent on the pH and the presence of dispersant. The increase in the initial pH of the solution above 7 and/or the addition of NH₄PA markedly reduced the Ca⁺⁺/H⁺ exchange reaction rate. As a result, well-stabilized concentrated aqueous suspensions could be obtained at pH close to 9. The minimum viscosity of 40 vol.% slips at pH 8.9 occurred at 0.6 wt% of NH₄PA added. The addition of 0.5 wt% PVA to a well-stabilized FA slip caused aggregation of particles by a depletion flocculation mechanism, thereby increasing the slip viscosity. The greater permeability of cakes produced from slips with high viscosity values (0.5 wt% PVA) increased the casting rate. The highest sintered densities were obtained for the compacts prepared from the slips without PVA, due to the denser particle packing achieved in the green bodies.     

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.     

Chemical activation of calcium aluminate cement composites cured at elevated temperature

The influence of sodium sulfate, as an activator, on the hydration of calcium aluminate cement (CAC)–fly ash (FA)–silica fume (SF) composites was investigated. Different mixes of CAC with 20% pozzolans (20% FA, 20% SF and 10% FA + 10% SF) were prepared and hydrated at 38 °C for up to 28 days. The hydration products were investigated by XRD, DSC and SEM. The results showed that sodium sulfate accelerated the hydration reactions of calcium aluminate cement as well as the reactions of FA and SF with CAH₁₀ and C₂AH₈ to form the strätlingite (C₂ASH₈). The later reactions prevent the strength loss by preventing the conversion of CAH₁₀ and C₂AH₈ to the cubic C₃AH₆ phase. The acceleration effect of Na₂SO₄ on the reactivity of fly ash was more pronounced than on the reactivity of silica fume with respect to reaction with CAH₁₀ and C₂AH₈ phases.     

Formation and properties of magnesium–ammonium–phosphate hexahydrate biocements in the Ca–Mg–PO<Subscript>4</Subscript> system

Calcium substituted trimagnesium phosphate with the general formula Ca_xMg_(3−x)(PO₄)₂ (0 < x < 1.5) was synthesized by calcination of powder mixtures with the appropriate stoichiometry and reacted with 3.5 M diammonium hydrogenphosphate solution to form a cementitious matrix of magnesium ammonium phosphate hexahydrate (struvite). The degree of ionic substitution was shown to influence physical cement properties; clinically suitable cement formulations with setting times in the range 5–15 min and compressive strengths of >50 MPa were obtained for x ≤ 0.75 together with a grinding time ≥1 h and a powder to liquid ratio ≥2.5 g/ml. The cement cytocompatibility was investigated by culturing human osteoblast cell line MG63 on cement surfaces demonstrating pronounced cell growth during 13 days cultivation.     

Chemical activation of calcium aluminate cement composites cured at elevated temperature

The influence of sodium sulfate, as an activator, on the hydration of calcium aluminate cement (CAC)–fly ash (FA)–silica fume (SF) composites was investigated. Different mixes of CAC with 20% pozzolans (20% FA, 20% SF and 10% FA + 10% SF) were prepared and hydrated at 38 °C for up to 28 days. The hydration products were investigated by XRD, DSC and SEM. The results showed that sodium sulfate accelerated the hydration reactions of calcium aluminate cement as well as the reactions of FA and SF with CAH₁₀ and C₂AH₈ to form the strätlingite (C₂ASH₈). The later reactions prevent the strength loss by preventing the conversion of CAH₁₀ and C₂AH₈ to the cubic C₃AH₆ phase. The acceleration effect of Na₂SO₄ on the reactivity of fly ash was more pronounced than on the reactivity of silica fume with respect to reaction with CAH₁₀ and C₂AH₈ phases.     

Mullite-zirconia composites: Effect of citric acid addition on slip and cast properties

Dispersion of mixed suspensions of zircon and α -alumina using citric acid as dispersant followed by pressure filtration produced after sintering (1600^∘C—2 h) dense mullite-zirconia composites. The effect of citric acid addition and pH on the rheological behavior of the mixed suspensions (57 vol%) was examined. Most of flow curves showed a shear thinning behavior at low shear rates reaching the viscosity a plateau at high shear rates. Newtonian viscosity at high shear rates values decreased to a minimum and then increased with increasing the amount of dispersant added. Compacts prepared from well stabilized suspensions achieved a maximum relative density of 72% (theoretical) which is slightly higher than that obtained from suspensions dispersed with a polyelectrolyte. Characteristics of sintered compacts such as density and crystalline phase composition by XRD were determined.     

Influence of fly ash as a cement addition on the hardened properties of recycled aggregate concrete

The effects of the use of Class F fly ash as a cement addition on the hardened properties of recycled aggregate concrete were determined. In this study, four series of concrete mixtures were prepared with water-to-cement (w/c) ratios of 0.55, 0.50, 0.45 and 0.40. The recycled aggregate was used as 0%, 20%, 50% and 100% replacements of coarse natural aggregate. Furthermore, fly ash was employed as 0% and 25% addition of cement. Although the use of recycled aggregate had a negative effect on the mechanical properties of concrete, it was found that the addition of fly ash was able to mitigate this detrimental effect. Also, the addition of fly ash reduced the drying shrinkage and enhanced the resistance to chloride ion penetration of concrete prepared with recycled aggregate. Moreover, it was found that the drying shrinkage and chloride ion penetration decreased as the compressive strength increased. Compared with the results of our previous study, the present study has quantified the advantages of using fly ash as an additional cementitious material in recycled aggregate concrete over the use of fly use as a replacement of cement.     

Microstructure and mechanical properties of accelerated sprayed concrete

Considering the different hydration processes of concrete without accelerator, sprayed concrete with low-alkali accelerator not only presents short setting times and high early-age mechanical properties but also yields different hydration products. This study presents an analysis of the mechanical properties of concrete with and without accelerator and sprayed concrete with three water–binder (w/b) ratios and four dosages of fly ash (FA) after different curing ages. It also examines the setting time, mineral composition, thermogravimetric–differential scanning calorimetry curves and microscopic images of cement pastes with different accelerator amounts. Furthermore, the setting time and microstructure of accelerated sprayed concrete with different w/b ratios and FA contents are examined. Results show that the retarded action of gypsum disappears in the accelerated cement–accelerator–water system. C₃A is quickly hydrated to form calcium aluminate hydrate (CAH) crystals, and a mesh structure is formed by ettringite, albite and CAH. A large amount of hydration heat improves the hydration rate of the cement clinker mineral and the resulting density, thereby improving mechanical properties at early curing ages. The setting times of the pastes increase with increasing w/b ratio and FA dosage. Thus, the hydration level, microstructure and morphology of the hydration products also change. Models of mechanical properties as functions of w/b, FA and curing age, as well as the relationship between compressive strength and splitting tensile strength, are established.