High-range Water Reducer Dosage Research Articles

Homogeneous flow performance of steel-fiber reinforced self-consolidating concrete for repair application: A biphasic approach

In this study, fiber-reinforced self-consolidating concrete (FR-SCC) was considered as a diphasic suspension of fiber and coarse aggregate (F-A ≥ 5 mm) skeleton in mortar suspension with solid particles finer than 5 mm. The coupled effect of the volumetric content of fibers, coarse aggregate particle-size distribution, and rheological properties of the mortar on the passing ability and dynamic stability of various FR-SCC mixtures was investigated. Nine high-strength and 10 conventional-strength FR-SCC mixtures for repair application were proportioned with water-to-binder ratios (W/B) of 0.35 and 0.42, respectively, and macro steel fibers of 0.1%–0.5% volumetric contents. The dosages of high-range water-reducer (HRWR) admixture were optimized to achieve a targeted slump flow of 680 ± 20 mm. The yield stress and plastic viscosity of the mortar mixtures varied between 4.6-17.7 Pa and 2.8–8.2 Pa s, respectively. Flow performance of the investigated mixtures were evaluated in terms of flowability (slump-flow test), passing ability (J-Ring and L-Box set-ups), and dynamic stability (T-Box test). According to the established correlations, the main influencing parameters on homogeneous performance of FR-SCC include W/B, paste volume, volumetric content-to-packing density of F-A (φ/φmax), HRWR dosage, fiber content, mortar rheology, and volume of excess mortar. The robustness analyses results revealed that homogeneous flow performance of FR-SCC is more sensitive due to variations of the φ/φmax and paste volume rather than mortar rheology, W/B, and HRWR dosage. The characteristics of the mixture constituents for FR-SCC mixtures with different strength levels were finally recommended to ensure acceptable homogeneous performance under restricted flow conditions of repair application.

Coupled effect of fine mortar and granular skeleton characteristics on dynamic stability of self-consolidating concrete as a diphasic material

Dynamic segregation of 30 self-consolidating concrete (SCC) mixtures proportioned with low and normal binder contents was evaluated using T-Box set-up. SCC was considered as a diphasic suspension of coarse particles (>1.25 mm) in Bingham fine mortars (<1.25 mm). The investigated fine mortar mixtures were characterized in terms of workability and visco-elastoplastic properties. The dynamic segregation of the investigated SCC mixtures was found in good agreement with the flow properties of their corresponding fine mortars, including mini-slump flow, yield stress, plastic viscosity, critical strain, storage, and loss moduli values, as well as the relative solid-packing fraction (φ/φmax) of coarser portion of granular skeleton (>1.25 mm). Optimizing the paste volume and φ/φmax of coarse aggregate, rather than adjusting the water-to-binder ratio and high-range water-reducer dosage, was shown to be more effective in enhancing the dynamic stability of SCC. Furthermore, higher dynamic segregation of coarser particles was observed due to shear-induced changes in grading of granular skeletons. Trade-offs between the flowability, passing ability, static, and dynamic stability characteristics of the investigated SCC mixtures were established. Accordingly, a new comprehensive workability-based classification was proposed. According to the proposed approach, four normal- and one low-binder SCC mixtures with high stability and medium-to-high filling ability properties were identified.

Onset and intensity of shear thickening in cementitious suspensions – A parametrical study

Understanding the intensity and onset of the shear thickening behaviour for cementitious suspensions is of prime importance in high shear processes like mixing and pumping of concrete in construction. In the present study, the onset and intensity of shear thickening of cementitious suspensions were investigated by a parametrical approach (water binder ratio (w/b), high range water reducer (HRWR) dosage, mineral admixture, shear rate) using an appropriate rheological protocol. Results show that, among the mineral admixtures, the suspension with ground granulated blast furnace slag (GGBS) features the highest shear thickening intensity and the earliest onset of shear thickening with respect to HRWR dosage. Moreover, this investigation shows that, among all the investigated parameters, the HRWR dosage influences the intensity and onset of shear thickening profoundly.

Relating the Electrical Resistance of Fresh Concrete to Mixture Proportions.

Characterization of fresh concrete is critical for assuring the quality of our nation's constructed infrastructure. While fresh concrete arriving at a job site in a ready-mixed concrete truck is typically characterized by measuring temperature, slump, unit weight, and air content, here the measurement of the electrical resistance of a freshly cast cylinder of concrete is investigated as a means of assessing mixture proportions, specifically cement and water contents. Both cement and water contents influence the measured electrical resistance of a sample of fresh concrete: the cement by producing ions (chiefly K+, Na+, and OH-) that are the main source of electrical conduction; and the water by providing the main conductive pathways through which the current travels. Relating the measured electrical resistance to attributes of the mixture proportions, such as water-cement ratio by mass (w/c), is explored for a set of eleven different concrete mixtures prepared in the laboratory. In these mixtures, w/c, paste content, air content, fly ash content, high range water reducer dosage, and cement alkali content are all varied. Additionally, concrete electrical resistance data is supplemented by measuring the resistivity of its component pore solution obtained from 5 laboratory-prepared cement pastes with the same proportions as their corresponding concrete mixtures. Only measuring the concrete electrical resistance can provide a prediction of the mixture's paste content or the product w*c; conversely, when pore solution resistivity is also available, w/c and water content of the concrete mixture can be reasonably assessed.

Optimization and performance of cost-effective ultra-high performance concrete

This paper presents a mix design method for ultra-high performance concrete (UHPC) prepared with high-volume supplementary cementitious materials and conventional concrete sand. The method involves the optimization of binder combinations to enhance packing density, compressive strength, and rheological properties. The water-to-cementitious materials ratio is then determined for pastes prepared with the selected binders. The sand gradation is optimized using the modified Andreasen and Andersen packing model to achieve maximum packing density. The binder-to-sand volume ratio is then determined based on the void content, required lubrication paste volume, and compressive strength. The optimum fiber volume is selected based on flowability and flexural performance. The high-range water reducer dosage and w/cm are then adjusted according to the targeted mini-slump flow and compressive strength. Finally, the optimized UHPC mix designs are evaluated to determine key properties that are relevant to the intended application. This mix design approach was applied to develop cost-effective UHPC materials. The results indicate that the optimized UHPC can develop 28-days compressive strength of 125 MPa under standard curing condition and 168–178 MPa by heat curing for 1 days Such mixtures have unit cost per compressive strength at 28 days of 4.1–4.5 $/m3/MPa under standard curing.

Rheology of belite-cement – Effect of w/c and high-range water-reducer type

The rheological properties of concrete determine its flow performance and thus they are of great importance in placement and consolidation. A full understanding of the behavior of fresh concrete can be achieved through a good understanding of the rheology of paste. Cement pastes exhibit complex rheological behavior affected by several physical and chemical factors, including water-to-cement ratio (w/c), type and dosage of high-range water-reducer (HRWR), and cement characteristics. An experimental investigation was carried out to investigate the rheological properties of belite cement (BC) mixtures made with various w/c ranging between 0.30 and 0.36 and two different types of HRWR. A polynaphthalene sulfonate (PNS) and a polycarboxylate-(PC) based HRWR were evaluated. Test results indicated that the use of BC in low w/c mixtures resulted in shear-thickening behavior when PC is employed and shear-thinning response for higher w/c. Compared to ordinary Portland cement (OC), the use of BC resulted in lower shear-thickening response, regardless of the w/c and HRWR type. The use of PC HRWR promoted the shear-thickening responses of mixtures for both types of cement. On the other hand, the use of PNS in combination with BC resulted in high yield stress values.

Flow characteristics of ternary blended self-consolidating cement mortars incorporating palm oil fuel ash and pulverised burnt clay

This article aims at investigating the flow characteristics of self-consolidating cement mortars incorporating palm oil fuel ash (POFA) and pulverised burnt clay (PBC). These mortars were tested with respect to their flow spread. Fifteen (15) different cement mortar mixtures were prepared containing Ordinary Portland Cement (OPC) and a blend of POFA and PBC at 0%/0%, 5%/5%, 10%/5%, 10%/10% and 15%/15% as a replacement of OPC. Water-to-binder ratio (W/B) of 0.3, 0.35 and 0.4 were used in all the mortar mixtures. The flow spreads of the mortars were determined using a standard flow mould and subsequently the relative flow areas were measured. The effects of different W/B, high range water reducer (HRWR) dosage and the blend percentage of POFA and PBC on flow characteristics of the various mortars were analysed and reported. Results showed that the flow of the mortar increased with the increase in POFA/PBC content and HRWR dosage while it decreased at higher W/B. Nonetheless, higher dosage of HRWR resulted in the bleeding of mortar. This study also showed that blended POFA/PBC can be used up to 30% replacement with a maximum HRWR content of 2.5% to design and produce self-consolidating cement mortar and concrete.

Effect of solid concentration and shear rate on shear-thickening response of high-performance cement suspensions

Flow performance, placement, and consolidation of concrete are mainly related to its rheology. Rheology of paste plays a key role on rheology of concrete. Cement pastes exhibit complex rheological behavior affected by several physical and chemical factors, including the solid concentration, type and dosage of high-range water-reducer (HRWR), cement characteristics, and shear history. An experimental investigation was carried out to investigate the effect of solid concentration, HRWR–cement combinations, and shear rate regime on pseudoplastic behavior of high-performance cement grouts. Grout mixtures proportioned with w/c of 0.30, various cement–HRWR combinations, 8% silica fume, and different limestone powder additions were investigated.Solid concentration and shear rate regime are shown to be key factors affecting shear-thickening response of concentrated cement-based suspension (i.e. low w/c). Concentrated high-performance grout mixtures are shown to exhibit shear-thickening behavior. The use of polycarboxylate HRWR acting by hindrance effect exhibited greater shear-thickening behavior compared to polynaphtalene type acting by electrostatic effect. The use of finer particles enhances the powder skeleton and ensures polydisperse systems, hence resulting in lower shear-thickening response. For concentrated cement-based suspensions, shear-thickening is due to disorder state, and at higher shear rate, hydrocluster formation is prevailing.

Flowing ability of self-consolidating concrete and its binder paste phase including palm oil fuel ash

The flowing abilities of different self-consolidating concrete (SCC) mixes and their binder paste phases including palm oil fuel ash (POFA) are presented in this paper. SCC mixes were produced with several water/binder (W/B) ratios and POFA contents. The binder pastes were formulated from their parent SCC mixes. The flowing abilities of SCC mixes were measured with respect to slump flow, T50 slump flow time, inverted slump cone flow time and V-funnel flow time. The flowing abilities of binder pastes were determined with regard to the flow times at various dosages of high-range water reducer (HRWR). The experimental results revealed that the W/B ratio, POFA content and HRWR dosage have significant influences on the flowing abilities of both SCC and binder paste. The research findings also showed that excellent correlation exists between the flowing abilities of SCC and its binder paste phase.

Correlations between Different Hardened Properties of High-Strength Self-Consolidating Concrete Including Palm Oil Fuel Ash

Palm oil fuel ash is considered as an agro-waste material in Malaysia. Various investigations have been conducted on the use of palm oil fuel ash as a supplementary cementing material for concrete. In the present study, palm oil fuel ash was used as a partial replacement of normal portland cement to produce high-strength self-consolidating concrete. In total, twenty (20) self-consolidating concrete mixes were prepared by varying water to binder ratio, palm oil fuel ash content, and high-range water reducer dosage. Palm oil fuel ash was used by replacing 0–30% of normal portland cement by weight at the water to binder ratios ranging from 0.25 to 0.40. The compressive, splitting tensile and flexural strengths, modulus of elasticity, ultrasonic pulse velocity, and porosity of various self-consolidating concrete mixes were investigated. However, the correlations between the hardened properties of concrete were emphasized in this study. The experimental findings revealed that strong correlations exist between different hardened properties of high-strength self-consolidating concrete.

Flowing ability of the mortars formulated from self-compacting concretes incorporating rice husk ash

This paper presents the flowing ability of the mortars formulated from various self-compacting concretes (SCCs) incorporating rice husk ash (RHA). The mortars were produced with different RHA contents and water–binder (W/B) ratios, as used in their parent SCCs. The flowing ability of the mortars was determined with respect to the flow spread at various dosages of a polycarboxylate based high-range water reducer (HRWR). The effects of RHA, W/B ratio, and HRWR on the flowing ability of mortars were observed. The mortar flowing ability decreased with the higher RHA content and W/B ratio, but increased with the greater HRWR dosage. However, the excessive HRWR dosages were not conducive to the mortar flowing ability due to the segregation problem in the form of bleeding. The overall mortar flowing ability results were useful to examine the suitability of RHA, and to fix the HRWR dosages for different SCCs.

Correlating Rheology of Self-Consolidating Concrete to Corresponding Concrete-Equivalent Mortar

The investigation reported in this paper seeks to develop a methodology to evaluate the rheological parameters and thixotropy of self-consolidating concrete (SCC) using those of concrete-equivalent mortar (CEM). The mixture proportioning of CEMs are derived from their corresponding concrete mixtures by eliminating the coarse aggregate fraction and replacing it by a certain mass of sand of the same surface area. SCC mixtures with water-cementitious material ratios (w/cm) of 0.35, 0.38, and 0.42 and coarse aggregate-total aggregate volume ratios (CA/A) of 0.44 to 0.53 were investigated. The mixtures with a w/cm of 0.38 and 0.42 incorporated low and moderate dosages, respectively, of a viscosity-modifying admixture to enhance stability. For each SCC, the dosage of high-range water-reducer (HRWR) was varied to cover a wide range of slump flow consistencies ranging between 570 and 730 mm (22.4 and 28.7 in.). All SCC mixtures were proportioned with 450 kg/m 3 (758.5 lb/yd 3 ) of ternary silica fume-ground granulated blast-furnace slag cement. A simple method is also proposed to determine the HRWR demand of SCC from that of the corresponding CEM. Test results showed that a good correlation can be established between the yield stress, plastic viscosity, and thixotropy of SCC and their corresponding CEM mixtures. Both thixotropy and plastic viscosity of SCC mixtures and their corresponding CEM mixtures are shown to vary primarily with variations in the w/cm and relative volume of coarse aggregate.

Properties of Concrete Containing Ultra-Fine Fly Ash

Fly ash and silica fume are two pozzolans that have been widely used for improved concrete strength and durability. Silica fume displays a greater pozzolanic reactivity than fly ash primarily due to its finer particle size. The reactivity of fly ash can be improved by reducing its particle size distribution. This paper discusses the fresh and hardened properties of concrete made with an ultra-fine fly ash (UFFA) produced by air classification. Durability testing for chloride diffusivity, rapid chloride permeability, alkali-silica reaction (ASR), and sulfate attack was also conducted It was found that at a given workability and water content, concrete containing UFFA could be produced with only 50% of the high-range water-reducer dosage required for comparable silica fume concrete. Similar early strengths and durability measures as silica fume concrete were observed when a slightly higher dosage of UFFA was used with a small reduction (10%) in water content.

Experiment design to evaluate interaction of high-range water-reducer and antiwashout admixture in high-performance cement grout

The injection of cement grout in water-saturated medium and the sealing of anchorages require the use of grout with high resistance to water dilution to enhance in-situ performance. This can be achieved by reducing the W/C and incorporating an antiwashout admixture (AWA) to enhance the stability. Such admixture can increase the viscosity and yield stress and necessitate higher dosage of high-range water-reducer (HRWR) to maintain the desired fluidity. Cement-based grouts with 0.30 to 0.50 W/C and different combinations of AWA and HRWR were evaluated. The study was undertaken to highlight the influence of W/C and dosage of chemical admixtures on fluidity, washout resistance, and residual compressive strength (RCS) of the underwater-cast grout. Statistical models established using a statistical design of experiments indicate that the W/C has greater effect on changes in minislump flow, washout, and RCS than the concentrations of HRWR and AWA. On the other hand, for mixtures prepared with a fixed W/C of 0.40, the models show that measured responses are highly affected by the dosages and interaction of both admixtures. Trade-off between fluidity and washout resistance and means to optimize mixture proportioning to enhance the resistance to water dilution without adversely affecting fluidity are discussed.

High-performance cement grout for underwater crack injection

An investigation was carried out to compare the performance of cement and epoxy resin grouts used for the underwater crack injection of four damaged concrete bridge pier shafts and footings. A blended silica fume cement and microfine cement and a welan gum and a cellulose-based antiwashout admixtures were considered in the grout optimization study. The mixtures were tested for fluidity, viscosity, stability, penetrability, rate of setting, and strength. This paper presents the results of the laboratory evaluation and field repair, including provisions adopted for surface preparation, crack sealing and injection, and quality control. Test results showed that the use of a microfine cement grout with water-to-cement ratio of 0.6 and a high-range water reducer dosage of 2% can produce a balance between critical rheological and mechanical properties. Such grout was found to be tolerant to changes in water-to-cement ratio, high-range water reducer content, and temperature. The grout developed bond strength to submerged concrete similar to that of a high-quality epoxy resin. Despite the lower injection pressure used for the less viscous cement-based grout, the grout intake was 2.8 times greater per linear meter of surface crack than that observed for the epoxy resin grout. The use of sonic tomography to reconstitute the spatial distribution of stress wave velocities within the massive pier footings indicated that the quality of concrete was significantly improved following injection with cement-based grout. This was attributed to the high penetrability of the microfine cement grout. Such quality improvement was less pronounced in the case of injection grouting with epoxy resin. Resume : Une Otude a OtO entreprise afin de comparer la performance des coulis ‡ base de ciment et ‡ base de rOsine-Opoxie utilisOs pour liinjection sous lieau des fissures dans le fst et liempattement de quatre piliers de pont. Un ciment avec fumOe de silice, un ciment microfin, une gomme welan et un autre agent anti-lessivage ‡ base de cellulose ont OtO considOrOs dans lioptimisation du coulis. Les mOlanges ont OtO testOs pour leur fluiditO, viscositO, stabilitO, pOnOtrabilitO, taux de prise, et

Effect of Welan Gum-High-Range Water Reducer Combinations on Rheology of Cement Grout

The effects of combined additions of welan gum, a commonly used rheology modifier, and naphthalene-based high-range water reducer on the rheological properties of cement grouts are investigated for mixtures made with 0.40 water-to-cement ratios. Grouts with dosages of rheology-modifying admixture varying from 0 to 0.075 percent by mass of cement were prepared. For each group of grout, the concentration of high-range water reducer was varied to obtain four mixtures of various fluidity levels. Measured properties included apparent viscosities at different shear rates, and estimates of plastic viscosity and yield value. Other measurements of consistency included the ease of spread and flow of grout evaluated using the mini-slump and Marsh cone tests, respectively. The grout stability was evaluated by measuring its resistance to water dilution when cast in water as well as its ability to retain water when subjected to sustained pressure (forced bleeding). Initial setting times were determined for selected mixtures. In all, a total of 27 grout mixtures were evaluated. Test results show that the increase in the dosage of rheology-modifying admixture increases significantly the yield value and plastic and apparent viscosities of cement grouts. Combined with an adequate dosage of high-range water reducer, losses in fluidity are regained without significant reduction in stability. With the increase in high-range water reducer dosage, the apparent viscosity at low rates of shear decreases more dramatically than that at high rates of shear due to the pseudo-plastic behavior of such grouts. The combined use of proper dosages of rheology-modifying admixture and high-range water reducer is shown to clearly contribute to securing high-performance cement grout that is highly fluid, yet cohesive enough to reduce water dilution and enhance water retention. For equal fluidity level, greater stability is obtained with mixtures containing high contents of viscosity modifying admixture. The initial setting time is shown to be delayed by the incorporation of high-range water reducer and rheology-modifying admixture with the latter additive exhibiting greater influence on retardation of setting.