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This study evaluates the potential to use shrinkage-reducing admixture (SRA) and pre-saturated lightweight sand (LWS) to shorten the external moist-curing requirement of ultra-high-performance concrete (UHPC), which is critical in some applications where continuous moist-curing is challenging. Key characteristics of UHPC prepared with and without SRA and LWS and under 3 days, 7 days, and continuous moist curing were investigated. Results indicate that the combined incorporation of 1% SRA and 17% LWS can shorten the required moist-curing duration because such a mixture under 3 days of moist curing exhibited low total shrinkage of 360 µε and compressive strength of 135 MPa (19,580 psi) at 56 days, and flexural strength of 18 MPa (2610 psi) at 28 days. This mixture subjected to 3 days of moist curing had a similar hydration degree and 25% lower capillary porosity in paste compared to the Reference UHPC prepared without any SRA and LWS and under continuous moist curing. The incorporation of 17% LWS promoted cement hydration and silica fume pozzolanic reaction to a degree similar to extending the moist-curing duration from 3 to 28 days and offsetting the impact of SRA on reducing cement hydration. The lower capillary porosity in the paste compensated for the porosity induced by porous LWS to secure an acceptable level of total porosity of UHPC. [ABSTRACT FROM AUTHOR]

Successful implementation of extrusion-based three-dimensional (3-D) printing requires the development of print materials with adapted rheology. In this study, filtration characteristics coupled with rheological properties of mortar mixtures are investigated to characterize the extrudability of print materials and establish a "printability window" (that is, the acceptable range of material properties for successful extrusion and shape stability). The extrudability was measured as the maximum force needed for the ram extrusion of the material. The fluid filtration rate was assessed in terms of desorptivity of the fresh mixture under pressure. The yield stress, plastic viscosity, and desorptivity were varied by changing the water-cement ratio (w/c), high-range water-reducing admixture (HRWRA) dosage, and welan gum (WG) content. Regression analysis indicated that during extrusion-based printing, the yield stress and desorptivity values can exhibit a more significant effect on extrudability than plastic viscosity. [ABSTRACT FROM AUTHOR]

This paper investigates the coupled effect of functionalized multi-walled carbon nanotubes (MWCNTs-COOH), nanomontmorillonite (NM), and sodium dodecylbenzene sulfonate (SDBS) anionic surfactant on compressive and flexural strengths of cement paste. The response surface methodology (RSM) was used to optimize the content of the two nanomaterials and surfactant, and to analyze the effect of their interactions on the mechanical properties and microstructural characteristics of the paste. Test results indicate that the simultaneous use of NM and MWCNTs can lead to a 30% gain in compressive strength and a 40% increase in flexural strength. Using analysis of variance (ANOVA), it was possible to predict the optimal weight percentage of nanomaterials. Atomic force microscope observations showed that the use of NM and MWCNT can reduce the surface roughness of cement paste and refine porosity, thus reducing the risk of cracking at the cement matrix and improving the homogeneity of the microstructure. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of the dosage rate of polycarboxylate ether (PCE) high-range water-reducing admixture and the water-powder ratio (w/p) on the rheological properties of cement paste added with 10% limestone powder. Qualitative approaches describing particle flocculation and energy dissipation mechanisms that can influence rheological properties are proposed by taking into account the degree of contact between the powder particles and the surface coverage of the powder particles by the PCE polymer. Test results show that the variations of the yield stress and viscosity of the cement pastes with changes in the w/p and PCE dosage are essentially affected by the coupled effect of the particle contact and surface coverage. Particle contacts can be enhanced by reducing the w/p. With the decrease of the w/p, the surface coverage of the powder particles decreases for a given PCE dosage, while it increases with the increase of the PCE dosage, indicating a reduction in colloidal interactions. Particle flocculation can be weakened as a combined result of the decrease in colloidal interactions and the enhancement of particle contacts. This can reduce the energy dissipated to break the internal particle network to initiate the flow of the cement paste and yield stress. Moreover, the energy dissipation inside the interstitial fluid between the powder particles can decrease with the increase of the surface coverage of the powder particles by the PCE. This can reduce the energy dissipation needed to maintain the flow of cement paste, despite the enhancement of the particle contacts. Residual viscosity is shown to decrease with the reduction of energy dissipation. [ABSTRACT FROM AUTHOR]

The prediction of concrete pumpability is of particular interest to properly design pumping circuits and select suitable pumps for successful processing of concrete. A critical review of empirical, analytical, and numerical models is carried out to predict concrete pumpability as a function of pipeline geometry, rheological properties of the bulk concrete, and the characteristics of the lubrication layer. The main mechanisms leading to the formation of the lubrication layer, including the wall effect, Reynolds dilatancy, and shear-induced particle migration (SIPM), are discussed. The main phenomenological models governing SIPM are formulated in terms of spatial variations of particles' interaction frequency and viscosity. In addition to the single-phase methodology, new computational approaches on SIPM in pipe flow of solid-liquid suspensions are discussed. The coupled computational fluid dynamicsdiscrete element method (CFD-DEM) and smoothed-particle hydrodynamics (SPH) methods are recommended as the most precise and realistic approaches to simulate concrete pipe flow compared to the DEM and single-phase modelings. [ABSTRACT FROM AUTHOR]

Fiber-reinforced high-strength grout (HSG) can secure exceptional mechanical properties; yet, case studies show that the interfacing layer to the existing substrate can be particularly vulnerable when used in specialty repair, precast, and retrofitting applications. Polymeric latex materials such as styrene-butadiene rubber (SBR) and acrylic ester (AE) are often incorporated to improve the bond properties and ensure monolithic behavior of the composite system. This paper assesses the concurrent effects of using steel fibers (SFs) and polymeric latexes on the flow and rheology of HSG, including their impact on mechanical properties and bond to existing concrete. The SF content varied from 0 to 5% by volume, while the mixing water was replaced by 10 to 20% of latex. Test results showed that the rheological properties of HSG increased with latex inclusion, given the coalescence of watersoluble polymers in the cementitious matrix that increased the viscosity of the interstitial liquid phase. The viscosity was aggravated with the addition of SF that accentuates the tendency of fiber grouping and interference between solid particles to hinder the ease of flow. The compressive strength slightly decreased when part of the mixing water was replaced by SBR or AE. Yet, in contrast, the flexural properties and pulloff bond strength were remarkably improved, which can be relevant to guarantee the integrity and monolithic behavior of the repair application. [ABSTRACT FROM AUTHOR]

An analytical model was established to predict the pumping pressure of flowable concrete as a function of flow rate, pipe diameter, and rheological properties of the concrete and the lubricating layer (LL). The flow behaviors of the different flow zones across the pipe section during pumping were analytically defined for Bingham materials. The prediction model was validated using a pumping circuit involving 14 high-strength flowable concrete mixtures with slump flow values of 500 to 765 mm. The rheological properties of the concrete and the yield stress, viscosity, and thickness of the LL (the latter determined through reverse regression analysis) were considered as input parameters in the prediction model involving 113 data points in the comparison. The analysis revealed that the thickness of the LL can vary between 2 and 5 mm, and that the predicted pressure loss agrees well with experimental measurements within the range of the tested mixtures. [ABSTRACT FROM AUTHOR]

Ultra-high-performance concrete (UHPC) can be vulnerable to variations in materials properties and environmental conditions. In this paper, the sensitivity of UHPC to changes in mixing, casting, curing, and testing temperatures ranging between 10 and 30 ± 2°C (50 and 86 ± 3.5°F) was investigated. The investigated rheological properties, mechanical properties, and shrinkage of UHPC are shown to be significantly affected by temperature changes. UHPC made with either binary or ternary binder containing fly ash (FA) or slag cement exhibited greater robustness than mixtures prepared with 25% silica fume. UHPC made with 60% FA necessitated the lowest high-range water-reducing admixture demand. With temperature increase, the yield stress of UHPC mixtures increased by up to 55%, and plastic viscosity decreased by up to 45%. This resulted in accelerating initial and final setting times by up to 4.5 and 5 hours, respectively. The increase of temperature from 10 to 30 ± 2°C (50 ± to 86 ± 3.5°F) led to a 10 to 75% increase in compressive, splitting tensile, and flexural strengths and modulus of elasticity and 15 to 60% increase in autogenous shrinkage. [ABSTRACT FROM AUTHOR]

The research presented in this paper addresses the effect of coarse recycled concrete aggregate (RCA) on drying shrinkage of concrete designated for transportation infrastructure. Six types of RCA were employed at 30 to 100% replacement rates of virgin coarse aggregate. Two binder systems, including a binary cement with 25% Class C fly ash and a ternary system with 35% fly ash and 15% slag were employed. Three different water-cementitious materials ratios (w/cm) of 0.37, 0.40, and 0.45 were considered. Test results indicate that the use of RCA increased drying shrinkage by up to 110% and 60% after 7 and 90 days of drying, respectively. Correlations with R2 of up to 0.85 were established to determine the shrinkage at 7, 28, 56, and 90 days as a function of aggregate properties, including specific gravity, water absorption, and Los Angeles abrasion resistance of the combined coarse aggregates. The water absorption of the combined coarse aggregate was shown to be a good index to showcase the effect of RCA on shrinkage. Contour graphs were developed to determine the effect of RCA content and its key physical properties on 90-day drying shrinkage of concrete intended for rigid pavement construction. A classification system available in the literature was also used to suggest the maximum allowable replacement rates for use of RCA in a hypothetical case study. Results suggest replacement rates of 100%, 70%, and 50% (% wt.) to limit the 90-day shrinkage to 500 μɛ when RCA of A-1, A-2, and A-3 Classes are available, respectively. [ABSTRACT FROM AUTHOR]

In this study, lightweight sand is used as an internal curing agent in ultra-high-performance concrete (UHPC). A factorial design approach was employed to evaluate the effects of multiple mixture proportioning parameters that are important for mixture optimization of UHPC. The investigated mixture design parameters included the substitution volume ratio of lightweight sand for river sand (LWS/NS: 0 to 25%), the cementitious materials-to-sand volume ratio (cm/s: 0.8 to 1.2), and the water-cementitious materials ratio (w/cm: 0.17 to 0.23). The evaluated properties included fresh properties, compressive strengths at up to 91 days, and autogenous shrinkage at up to 28 days. Statistical models that take into account the coupling effects of mixture proportioning parameters were formulated to predict the UHPC properties. The w/cm and LWS/NS were the most significant parameters influencing the compressive strength and autogenous shrinkage, respectively. By replacing the river sand with 25% lightweight sand, the compressive strength at 91 days increased from 150 to 170 MPa (22.5 to 25.5 ksi) and the autogenous shrinkage at 28 days decreased from 410 to 70 μm/m (410 × 10-6 to 70 × 10-6 in./in.). The mixture with w/cm of 0.23, LWS/NS of 0.25, and cm/s of 1.2 is determined as the optimum UHPC mixture. The material properties of the mixture: the HRWR demand was 0.6%, the 28-day autogenous shrinkage was 260 μm/m (260 × 10-6 in./in.), and the 91-day compressive strength was 147 MPa (22.1 ksi). [ABSTRACT FROM AUTHOR]

The reduction of cement content and incorporation of high volume of supplementary cementitious materials (SCMs) are key factors for the design of environmentally friendly concrete (Eco-Crete). The effectiveness of incorporating an SCM to enhance rheological and mechanical properties and durability of concrete depends on the type and content of SCM, as well as the degree of dispersion of the binder resulting from the use of high-range water reducer (HRWR). An experimental investigation was undertaken to evaluate the effect of binary and ternary cementitious materials on the packing density of the binder and compressive strength at 7 and 56 days of cement paste. The influence of the dispersion state of the binder on packing density was evaluated using the wet packing density approach to determine the optimum water demand (OWD) needed to achieve maximum wet density. The effectiveness of incorporating a high volume of SCM to enhance packing density is shown to increase with an increase of HRWR dosage, resulting from a greater degree of dispersion of the binder. The incorporation of sufficient dosage of HRWR led to lower OWD needed to achieve maximum density and higher packing density. The coupled effect of these changes results in higher compressive strength. Compared to the packing density of 0.58 for binder with 100% cement, the use of SCMs in a well-dispersed system is shown to secure packing density of 0.60 to 0.73. The ternary binders containing 40 or 50% slag and 5 or 10% silica fume, by volume of total binder, can ensure lower OWD, greater packing density, lower CO2 emission, and higher compressive strength. Such binder systems can be adopted for use in sustainable cement-based materials. [ABSTRACT FROM AUTHOR]

An extensive testing program was undertaken to evaluate the applicability of a mixture-proportioning method proposed for shrinkage control in fiber-reinforced concrete (FRC) in proportioning fiber-reinforced self-consolidating concrete (FR-SCC). The study also proposed test methods to evaluate workability of FR-SCC. The investigated fibers included polypropylene, steel, and hybrid fibers of different properties with fiber lengths of 5 to 50 mm (0.20 to 1.97 in.). Fiber volume Vf ranged between 0.25 and 0.75%. The study also aimed to determine the impact of fiber type and addition on key properties of the fresh and hardened concrete. Hardened properties included compressive, splitting tensile, and average residual strengths. Test results indicate that the proposed methodology to maintain constant mortar thickness over coarse aggregate and fibers can reduce any significant drop in workability of FR-SCC, resulting from an increase in fiber factor. In general, a Vf of 0.5% is found to be an upper limit for the production of SCC. A greater Vf can hinder the self-consolidating characteristics. For the assessment of the passing ability of FR-SCC, a modified J-ring setup containing six or eight bars instead of 16 bars is proposed. The passing ability of FR-SCC can be expressed as the ratio of diameter: height at the center of the J-ring test. The passing ability can also be evaluated using the L-box with a single bar instead of three bars. A superworkable concrete (SWC) requiring low consolidation energy can still be produced with a Vf of 0.75% when a viscosity-modifying admixture is incorporated to prevent segregation and blockage. For the tested fiber types, the average residual strength (ARS) in flexure is shown to increase with Vf. Steel fibers exhibited the highest ARS value. [ABSTRACT FROM AUTHOR]

In the case of casting deep elements, self-consolidating concrete (SCC) should be designed with high thixotropy to reduce lateral pressure on the formwork system and with low thixotropy in multilayer casting to avoid the formation of a weak interface between successive lifts. Therefore, thixotropy determination of SCC on site may be necessary. Thixotropy can be determined by evaluating the rate of structural buildup at rest. Quality control of SCC on site necessitates the use of a simple, robust, and inexpensive test. A field-oriented test (portable vane device) enabling the evaluation of the structural buildup at rest of concrete is highlighted in this paper. Relative errors between 4 and 20% are estimated for this device. Good correlations are observed between six indexes of structural buildup determined from the portable vane and concrete rheometer using 60 SCC mixtures. The classification of SCC mixtures according to thixotropic values and the ranking of the six structural buildup indexes are also introduced in this paper. [ABSTRACT FROM AUTHOR]

Given the sensitivity of self-consolidating concrete (SCC) to small variations in raw material characteristics, more care should be taken for the selection of constituent materials and mixture proportioning to secure adequate robustness. An experimental program was undertaken to evaluate the robustness of SCC subjected to variations in sand humidity. Eight groups of SCC mixtures with various combinations of viscosity-enhancing admixtures (VEAs) and high-range water-reducing admixtures (HRWRAs) were tested. For each group, mixtures with sand humidity corresponding to saturated surface-dry (SSD) condition and ±1% humidity were prepared. The tested mixtures were ranked in terms of robustness using the values of the coefficient of variation (COV) for all 20 of the properties investigated. A statistical approach was then used to reduce the number of properties that could provide a similar ranking of robustness. The test results show that the use of microbial anionic polysaccharide VEAs can provide greater robustness than cellulose-based VEAs. In the case of mixtures made without any VEA, SCC incorporating polynaphthalene sulfonate-based HRWRA was found to be more robust than similar SCC prepared with polycarboxylate ether-based HRWRA. [ABSTRACT FROM AUTHOR]

Viscosity-enhancing admixtures (VEAs) are water-soluble polymers that increase viscosity and cohesion of cement-based materials. Such enhancement is essential in highly flowable concrete — including self-consolidating concrete (SCC) —to control the risk of segregation. For a given mixture composition, the performance of SCC can widely vary with the type and dosage rate of the VEA in use. The main objective of this investigation is to compare the performance of five VEA systems in SCC. More specifically, the investigation seeks to determine the effect of VEA type on key workability and engineering properties of SCC designated for cast-in-place building applications. The concrete is designed with a characteristic compressive strength of 35 MPa (5076 psi) at 28 days. In total, five VEAs incorporated with two compatible high-range water-reducing admixtures (HRWRAs) are investigated. A finely ground limestone filler that can be used as a stabilizer in flowable concrete is also included in the study. [ABSTRACT FROM AUTHOR]

The proper evaluation of shrinkage is critical for the design of prestressed structural members. An experimental program was undertaken to evaluate autogenous and drying shrinkage of precast, prestressed self-consolidating concrete (SCC). Sixteen SCCs with a slump flow of 680 ± 20 mm (26.7 ± 0.8 in.) were evaluated. These mixtures were made with 440 to 500 kg/m³ (742 to 843 lb/yd³) of binder, Type MS cement or HE cement; and 20% Class F fly ash; 0.34 to 0.40 water-cementitious material ratio (w/cm); viscositymodifying admixture content of 0 to 100 mL/100 kg (0 to 1.53 fl oz/cwt) of binder, and 0.46 to 0.54 sand-to-total aggregate volume ratio. Two high-performance concretes (HPCs) with 0.34 and 0.38 w/cm and slump of 150 mm (5.9 in.) were also investigated. The SCC developed 5 to 30% higher drying shrinkage at 300 days than the HPC but with similar autogenous shrinkage. The shrinkage was compared to prediction models proposed by AASHTO 2004 and 2007, CEB-FIP 90, GL 2000, and ACI 209R. The CEB-FIP 90 and a modified AASHTO 2004 model was found to provide an adequate prediction of shrinkage for precast, prestressed SCC. [ABSTRACT FROM AUTHOR]

A comprehensive research project was undertaken to evaluate the effect of hydrostatic pressure and interfacial concrete/water velocity on the performance of underwater concrete (UWC) designated for repair applications. Washout loss was determined on 33 optimized mixtures using the CRD C61 test method, as well as a newly developed device enabling the simulation of concrete washout placed at various depths down to 140 m (460 ft) below water surface level. Test results showed that washout loss of UWC increases with the increase in water head. Depending on the mixture composition, a critical threshold water depth can be found, beyond which significant washout loss could take place. The effect of decreasing the interfacial concrete/water velocity from 2.5 to 0.5 m/s (8.2 to 1.6 ft/s) was found to reduce washout loss for a given depth of casting or enable the casting in deeper water for a given washout resistance. Good correlations were obtained between washout loss determined as per the CRD C61 test method and the washout loss derived from estimates given a certain interfacial concrete/water velocity and water depth. [ABSTRACT FROM AUTHOR]

The article focuses on the evaluation of the rheological parameters and the flow properties of self-consolidating concrete (SCC) through concrete-equivalent mortar (CEM). It presents an analysis on the behavior of the fresh SCC using mortar that contains 2 mm sand particles. It investigates the yield stress of the concrete and its plastic viscosity through the consideration of the micro-mortar phase of concrete mixtures. It also dwells on the discussion on the proposed relationship between SCC's slump flow and CEM. Moreover, it explores several factors that affect the performance of SCC including the reduction in free water content, paste volume increase and high-range water-reducer (HRWR) dosage. It proposes a new method to understand SCC's demand for HRWR from its corresponding CEM.

The article reports on the effect of mixture composition on restrained shrinkage cracking of self-consolidating concrete used in repair. It discusses that contributed mixture pattern, self-consolidating concretes (SCC) can inherently demonstrate greater risk of drying shrinkage and limited shrinkage cracking equated with normal decline consistency. It infers that with the indication in an increase in fiber volume can lead to a reduction in cracking potential of concrete regardless of its fiber type. An overview on consolidating concrete is also presented.

The article presents a study on the impact of temperature and time on rheological properties of cement-based materials. It targets to match the effects of time and temperature on the development of rheological parameters. The researchers use micromortars in the experiment to check the changes in yield stress and plastic viscosity. It is also mentioned that the temperature of the mortars after heat flux is observed. Moreover, they discover that yield stress and plastic viscosity alter in linear manner.

The article evaluates the impact of thixotropy-enhancing agent (TEA) on the variations in thixotropy and formwork lateral pressure of self-consolidating concrete with slump flow consistency. The study involves the testing of six mixtures containing various TEA concentrations along with either a melamine- or polycarboxylate-based high-range water-reducing admixture. Results indicated that the use of TEA can significantly increase the degree of thixotropy and reduce the framework pressure compared with similar mixtures containing conventional viscosity-enhancing admixtures.

The article presents a study that evaluated the static stability of flowing and self-consolidating (SCC) concrete. Due to the critical function of segregation of coarse aggregate in concrete materials in determining their mechanical properties, the study was conducted to develop a rapid methodology for estimating segregation during the dormant period of cement hydration using a multi-pair electrode conductivity method. Results of the segregation during cement hydration and actual segregation on hardened concrete showed a high degree of correlation. It was concluded that the conductivity approach is an effective tool in evaluating the static stability after concrete placement.

The article discusses a study which determines the effect of viscosity-enhancing admixtures (VEA) on the formwork pressure of self-consolidating concrete (SCC). The study used in the experimentation process both liquid and powder polysaccharide and cellulose-based VEA and engaged the high-range water-reducing admixtures (HRWRA). The result of the study showed that VEA-HRWRA has its effect in the formwork pressure of SCC.

This article reports on the experimental program undertaken to evaluate the effect of water-cementitious material ratio and type of high range water-reducing admixture on the development of form-work pressure that can be exerted when using self-consolidating concrete (SCC). It can be concluded from the test results that the variations in lateral pressure and thixotropy of SCC are significantly affected by water-cementitious material ratio.

The article evaluates the suitability of various test methods for workability assessment, and suggests performance specifications of concrete used in structural applications. The study shows a variation in workability characteristics for 70 self-consolidating concrete mixtures. Workability responses include the slump flow, J-Ring, V-funnel flow time, L-box, filling capacity, and surface settlement tests.

Reports on an experimental program to determine the effect of binder type and content on variations in lateral pressure of self-consolidating concrete (SCC). Preparation of the mixtures with five binder types; Influence of thixotropy on the variations of lateral pressure development; Increase in binder content resulting to a greater rate of gain in cohesiveness and a sharper drop in lateral pressure with time.

Studies the effect of coarse aggregate characteristics on lateral pressure exerted by self-consolidating concrete. Mixture preparation; Results of tests.

Studies the effect of thixotropy on the development of formwork pressure of self-consolidating concrete and concrete-equivalent-mortar. Effects of different types of binders on concrete mixtures; Protocols to quantify the degree of thixotropy.

Investigates the kinetics of variations in lateral pressure and pore water pressure that can be exerted by self-consolidating concrete during the plastic stage of cement hydration and until the early stage of hardening. Sand-to-total aggregate ratio; Rate of pressure drop; Degree of internal friction.

Presents several test methods used to evaluate the static stability of self-consolidating concrete (SCC) to ensure the uniform properties of the hardened material. Focus on the assessment for surface settlement, aggregate segregation and monitoring electrical conductivity changes; Investigation of sixteen SCC mixtures designed to provide specified slump flow values; Suitability of the methods for acquiring the stability over the dormant period, establishment of the coarse agrregate distribution and monitor the stability of mortar.

Discusses the comparison of field-oriented test methods to assess the dynamic stability of self-consolidating concrete. Process of casting the self-consolidating concrete; Criticality of selecting the effective test methods to assess stability; Elaboration of methods pertaining to dynamic stability.