Self-consolidating Concrete Mixtures Research Articles

Hardened property changes due to the pumping process of self-consolidating concrete

Pumping of self-consolidating concrete (SCC) is a vital construction technique. Curiosities are aroused by the effect of this intense physical process on the hardened properties of SCC. To examine this issue, a total of seven SCC mixtures are pumped at constant flow rates in pipelines with lengths of 324, 600, and 912 m. Parameters related to the hydration stages, air-void system, compressive strength, elastic modulus, and shrinkage at early ages are tested on specimens made of concrete before and after pumping. Results of tested samples find that the spacing factor grows, but the specific surface lessens after pumping. Also, in most cases, the compressive strength and elastic modulus decrease due to the pumping. The variations of these two factors are linearly related to the pumping distance in most cases. Additionally, the variations in the early age of shrinkage cracking show a dependency on the concrete compositions, temperature, and pumping characteristics.

Time-dependent rheological analysis of self-consolidating concrete mixtures considering various mixing temperatures

This study aims to investigate the effect of the temperature of the self-consolidating concrete (SCC) mixture during casting on fresh and hardened properties for two types of SCC. Also, the rheological properties of the mixtures were assessed at specific time intervals (0, 20 and 40 min after mixing) to determine their sensitivity to changes in mixtures’ properties and temperature over time. For this purpose, two categories of SCC were prepared: Powder type and Viscosity-Agent type. Silica fume, metakaolin (MK) and slag were utilised as substitutes for cement in these samples. The mixtures were tested at low and high temperatures of 5 °C and 34 °C, respectively, with an average temperature of 21 °C. Results indicated that as the mixture temperature decreased, the yield stress decreased by 30% and the plastic viscosity increased by 25% on average. Conversely, as the temperature increased, the yield stress increased by 20% and the plastic viscosity decreased by 40% on average. Moreover, increasing the mixture temperature resulted in a 10% increase in the 7-d compressive strength but a 15% decrease in the 28-d compressive strength of the specimens. Additionally, increasing the rest time after mixing increased the yield stress, while the plastic viscosity remained relatively stable with occasional increases.

Use of hybrid fibers and shrinkage mitigating materials in SCC for repair applications

Self-consolidating concrete (SCC) is used to repair structural elements with congested reinforcement or restricted access to placement and consolidation. In addition to adequate flowability, passing ability, filling capacity, and stability, adequate bonding to the substrate and reinforcing bars, low shrinkage and cracking resistance are required for successful repair. This study employs various shrinkage mitigating materials, including expansive agent (EA), coupled use of EA with shrinkage reducing admixture (SRA), and EA with pre-saturated lightweight sand (LWS) to fulfill these requirements. The effect of these materials on the performance of SCC made with a hybrid synthetic (PP) fiber and a hybrid steel-synthetic (STPP) fiber is investigated. The investigation included key fresh and hardened concrete properties and flexural performance of composite beams repaired using these materials. Test results show that the investigated fiber-reinforced self-consolidating concrete (FRSCC) mixtures can secure adequate workability and mechanical properties and low shrinkage, limited to 600 µstrain after 224 days. High EA content (10% by mass of binder) can lead to excessive expansion at early ages resulting in microcracking and drop in mechanical properties. The FRSCC made with 5% EA and 0.5% SRA, by mass of binder (5EA0.5SRA mixture), had superior mechanical properties (50 MPa compressive strength and 36 GPa modulus of elasticity). The cracking potential due to restrained shrinkage of this mixture is very low. The 5EA0.5SRA mixture made with hybrid synthetic fibers is successfully used to repair reinforced concrete beams prepared with various reinforcement ratios in the tension zone. The results indicate a 48% increase in first crack load, 4% gain in peak load, and 33% increase in flexural toughness compared to the monolithic beam cast with the conventional concrete. A comparison between the cracking load and ultimate flexural capacity of the repaired beams with estimated values by ACI 544 reveals the estimated to experimental ratio of 0.36–0.70 for cracking load and 0.56–0.74 for the flexural capacity. This can stem from the promotion of FRSCC concrete by the effect of hybrid synthetic fibers and the development of internally induced stress in the presence of shrinkage mitigating materials and fibers that led to higher mechanical properties and enhanced performance of FRSCC for repair. Reinforced beams repaired using FRSCC made with 0.5% hybrid synthetic fibers and combination of EA-SRA can reduce the steel reinforcement ratio by 21% to 27%, depending on the primary steel reinforcement.

Bond Strength of Reinforcing Steel Bars in Self-Consolidating Concrete

This paper presents an experimental investigation of the bond strength of reinforcing steel bars in tension in self-consolidating concrete (SCC). The effects of the reinforcing bar’s location, orientation, size, and coating on the bond strength with SCC were studied and compared to those with conventionally vibrated concrete (CVC). Several SCC mixtures were developed to cover a wide range of applications/components and material types. The fresh properties of the SCC mixtures were determined to evaluate their filling ability, passing ability and stability. Two hundred and thirty-four pull-out tests of rebars embedded in cubes, wall panels and slabs were conducted. Almost half of the tests were conducted to evaluate the bond with SCC and the other half with CVC. Load–slippage relationships were measured for each test. Pull-out test results were analyzed, and the bond strength was reported in two values: critical strength, which corresponds to slippage of 0.01 in. *0.25 mm); and ultimate strength, which corresponds to the maximum load. The critical strength of SCC and CVC were compared against the ACI 318-19 provisions and comparisons between the ultimate strength of SCC and CVC were conducted. The comparisons indicated that SCC has lower bond strength with vertical rebars than CVC, and a 1.3 development length modification factor is recommended. A similar conclusion applies to epoxy-coated and large diameter rebars. Also, SCC with high slump flow has shown a less top-bar effect than that of CVC.

Prediction of self-consolidating concrete properties using XGBoost machine learning algorithm: Part 1–Workability

The interest in implementing self-consolidating concrete (SCC) in major construction projects has increased significantly in recent years. This paper reports the results of an extensive survey of experimental data of more than 1700 SCC mixtures from over 100 studies published in the last decade. The survey included the SCC mixture proportioning, key fresh properties including flowability, passing ability, and segregation resistance, as well as some of the derived properties (e.g., paste volume). The statistical analysis of the reported parameters showed wide variations in values. The outcome of the survey indicates that SCC mixture design and workability properties do not systematically lie within the recommendations reported in various guidelines. A wide range of workability tests is used; however, only 22 % of the studies reported values for segregation resistance. The slump flow test was the most tested fresh property and the most reported values are in range of 591–760 mm (X¯ = 679 mm). The V-funnel time was the second most reported test, and the most of reported values are in range of 4.0–20 s (X¯ = 11 s). The study devised and evaluated the efficacy of using machine learning (ML) models, namely Extreme Gradient Boosting (XGBoost), to predict the two most reported workability characteristics of SCC, namely slump flow and V-funnel flow time. The model was formulated to predict slump flow and V-funnel time using a refined sub-database of 852 tests (the extreme data i.e., 5 % from each side, for the both properties and the empty data was deleted). The findings revealed that the XGBoost model can provide an accurate prediction for the slump flow and V-funnel values, thus indicating its potential as a powerful tool for SCC optimization. The findings provide valuable insights into the application of ML in SCC research and contribute to the development of more efficient and sustainable construction practices.

Hygrothermal and microstructural characterization of self-consolidating earth concrete (SCEC)

The incorporation of earth-based materials offers the construction industry superior hygrothermal performance, hence ensuring significant ecological and environmental benefits. The hygrothermal and microstructural characteristics of self-consolidating earth concrete (SCEC) are investigated in this study. These traits include the sorption isotherm, permeability, heat capacity, thermal parameters (conductivity, diffusivity, and effusivity), moisture buffer value (MBV), total porosity, pores distribution, and microstructural characteristics. The sorption isotherm tests revealed that the investigated SCEC mixtures gained lower water content (around half) compared with the reference self-consolidating concrete (SCC) mixture (1.5% vs. 3.3% at 90% relative humidity). These results are comparable to those reported for clay bricks in the literature. The SCEC mixtures also showed higher permeability due to their higher porosity and connected pores. Thermal conductivity, diffusivity, and effusivity of the investigated SCEC mixtures showed lower values than those of the reference mixture. At 10 °C, the investigated SCEC mixtures exhibited lower thermal conductivity values of 0.400–0.500 W m−1 K−1 compared with those of the reference mixture (0.765 W m−1 K−1). Since the diffusivity and effusivity of the earthen materials are higher than those of wood, SCEC mixtures can offer both low diffusivity and high effusivity among different construction materials. Furthermore, the investigated SCEC mixtures exhibited lower mass losses attributed to calcium silicate hydrate (CSH), dehydroxylation of portlandite, and decarbonation than the reference mixture. The water vapor and gas permeability of SCEC were in good agreement with cumulative pore volume in the ranges of 100–200 nm and 100–300 nm, respectively. On the other hand, the drying shrinkage and compressive strength values were dependent on the cumulative pore volume of pore sizes less than 1 μm.

Coupled effect of fiber and granular skeleton characteristics on packing density of fiber-aggregate mixtures

The addition of fiber to cementitious materials enhances mechanical performance but can reduce workability of the fiber-reinforced concrete (FRC) mixtures. This can be due to the negative effect of fibers on packing density (PD) of the fiber-coarse aggregate (F-A) combination. The performance of FRC, as a diphasic suspension, is dependent on the characteristics of both F-A (suspended-solid skeleton) and mortar (suspending liquid) phases. PD can reflect the voids within the F-A skeleton to be filled with mortar. An adequate optimization of the characteristics of the F-A skeleton can modify the performance of FRC in fresh and hardened states. The F-A skeleton can be characterized in terms of particle-size distribution, volumetric content, and morphology of the coarse aggregate, as well as size, rigidity, and content of fibers. In this study, a comprehensive investigation was undertaken to identify the coupled effect of the characteristics of fibers and coarse aggregate on the PD of F-A combination used without any cement paste/mortar. The solid components play a key role in the overall performance of the concrete produced. This study was carried out to optimize the F-A combination and enhance the workability design of FRC. Various types of steel, polypropylene, and polyolefin fibers having different sizes and rigidities were investigated. Moreover, four combinations of three different classes of coarse aggregate were used to proportion F-A mixtures. Test results showed that shorter length, smaller diameter, and more flexible fibers can lead to higher PD of F-A systems. Moreover, the coarser aggregate skeleton with larger interparticle voids led to more available length for fibers to be deformed, hence improving the PD of F-A mixtures. New empirical models were proposed to predict the packing density of F-A combinations given the characteristics of coarse aggregate and fibers, as well as the level of compaction. The established models were employed to propose a new proportioning approach for fiber-reinforced self-consolidating concrete mixtures to achieve the targeted workability.

Evaluation of self-consolidating concrete shear strength by means of push-off test

Self-consolidating concrete (SCC) can be characterised by its flowability, stability and passing ability. Although SCC tends to have a more uniform microstructure in the concrete–reinforcement interfacial transition zone, the reduction of the nominal size and coarse aggregate content in the concrete mix may adversely affect its shear strength. Therefore, the aim of this research was to evaluate the shear strength of SCC by means of push-off tests of 45 specimens, produced with one conventional concrete and two SCC mixtures, with two different coarse aggregate contents (reference and reduced by 30%). The transverse reinforcement ratio ranged from 0.46% to 2.28%, using closed stirrups crossing the shear plane. The increase of reinforcement ratio resulted in improvements in shear strength for specimens with one, two and three stirrups, while specimens with four and five stirrups had a premature failure owing to concrete crushing near the notch. No significant difference in shear strength was identified owing to concrete type or coarse aggregate. The experimental results were also compared with codes estimates, and Eurocode 2 presented the best fit to experimental results when compared with the American code ACI 318 and the Canadian standard CSA A23.3.

Influence of natural zeolite on fresh properties, compressive strength, flexural strength, abrasion resistance, Cantabro-loss and microstructure of self-consolidating concrete

This study aimed to evaluate the effect of natural zeolite (NZ) on some fresh and hardened properties of self-consolidating concrete (SCC). For this purpose, eight mixtures containing 0, 5%, 10%, and 15% NZ as partial replacement of portland cement with two water to binder ratios (w/b) were studied. In order to evaluate the mechanical properties of concrete, compressive strength and four-point bending tests were performed at the ages of 7, 28, and 90 days. The abrasion resistance and Cantabro-loss tests were performed according to ASTM C779-A (procedure A-revolving discs) and ASTM C1747, respectively at the ages of 28 and 90 days. The results indicated that the HRWR demand of SCC mixtures increases with NZ content. However, the viscosity and stability of the mixtures were improved by NZ. Overall, the mechanical properties of SCC mixtures were improved by using NZ. The optimum rate of NZ was found to be 10%. Although the reduction of the w/b ratio had a more significant effect on improving the mechanical properties compared to using NZ, the reduction of the w/b ratio along with the partial replacement of cement with NZ enhanced this effect. In addition, regression analysis showed a strong correlation between the results of abrasion resistance and Cantabro-loss tests. The results of SEM analysis showed a significant reduction in the width, length and number of micro-cracks in the bulk binder paste and the ITZ of 10% NZ mixtures compared to the plain portland cement mixtures. High peak intensities of C-S-H gel and low intensities of ettringite were also observed by XRD analysis in the ITZ of NZ- containing concretes due to pozzolanic reaction.

Feasibility study of implementing gamma-ray computed tomography on measuring aggregate distribution and radiation shielding properties of concrete samples

Aggregate segregation is one of the key defects that impair the performance of concrete at fresh and hardened stages. This study aims to assess the feasibility of using an advanced technique to identify/scan/determine the aggregate segregation of concrete elements and determine radiation shielding properties of the concrete. The gamma-ray computed tomography (γ-CT) technique was employed to study aggregate distribution/dispersion in self-consolidating concrete (SCC). Accordingly, two SCC mixtures with moderate segregation (MS) and high segregation (HS) levels were cast and compared with highly stable SCC with no segregation (NS). The γ-CT scans were located on three different levels of concrete specimens located at the top-level (L1), middle-level (L2), and bottom-level (L3). A Cs-137 (660 keV emission) was used as a gamma-ray source to measure the linear attenuation coefficient per unit chord length at each level. Alternating minimization (AM) algorithm was utilized for cross-sectional image reconstruction based on the attenuation coefficient of the material density and the elements atomic number that represent the materials. A phantom of three Plexiglas layers was used to pre-validate the technique’s ability to identify aggregate locations. Moreover, the γ-CT scans of the concrete samples were compared with selected sections using the image processing method. The findings confirmed that the γ-CT technique can determine the level of segregation in the investigated samples. Further, it has been found that the presence of the aggregate enhanced the radiation shielding properties by up to ∼25%. The linear attenuation values were used to quantify the aggregate distribution of the concrete samples.

Оценка предела прочности при сжатии в самоуплотняющемся бетоне, подверженному циклическому замораживанию и оттаиванию, с использованием ультразвукового импульсного метода

The development and use of self-consolidating concrete (SCC) considerably increased in the last decade. This work aims to evaluate the effect of using air-entraining admixture (AEA) on the compressive strength of SCC subjected to freeze-thaw (F-T) cycles. For comparison purposes, six mixtures were prepared with fixed powder content of 580 kg/m3 and sorted into two categories of unmodified and air-entrained SCC mixtures. For each category, the water-to-cement ratio (w/c) varied at 0.45, 0.5, and 0.56. The corresponding compressive strength and ultrasonic pulse velocity (UPV) measurements were carried out on samples before and after being subjected to 400 F-T cycles. Test results demonstrated that AEA enhanced the performance of SCC, particularly at lower rates of w/c. Air void characteristics records validate the enhanced performance for air-entrained SCC, given the air void system that accommodated the disruptive expansive stresses resulting from F-T cycles. Furthermore, the residual compressive strength of SCC can be accurately estimated by using UPV measurements.

Fresh, Durability and Mechanical Behavior of Self Consolidating Concrete Incorporating Fly Ash and Admixture under Hot Weather

The self-consolidating concrete (SCC) become the material of choice by concrete industry due to its superior properties. However, these properties need to be verified under hot weather conditions. The paper investigates the behavior of SCC under hot weather. Six SCC mixtures were prepared under high temperatures. The SCC mixtures incorporated polycarboxylate admixture at different dosages and prolonged mixed for up to 2 hours at 30 °C and 40 °C. The cement paste was replaced with 20% of fly ash (FA). The fresh properties were investigated using slump flow, T50, and VSI tests. The compressive strength was measured at 3, 7, and 28 days. The durability of SCC mixtures was evaluated by conducting rapid chloride penetration and water absorption tests.

Rheology and mechanical performance of self-consolidating hybrid-geopolymer concrete as a sustainable construction material

This investigation aimed to develop a new alkali-activated-based self-consolidating concrete (SCC) as a sustainable construction material. The rheological and hardened properties of hybrid matrix-based SCC (H-SCC) were assessed and discussed. The hybrid matrices were proportioned with optimum NaOH-activated fly ash and glass powder used as partial replacement of cement. The obtained results showed that the investigated hybrid SCC mixtures exhibited good flowability and passing ability. Furthermore, the H-SCC mixtures exhibited good static stability and low segregation. Although the hybrid SCC mixtures developed lower compressive strength than the reference SCC mixture, the obtained strength values were within the strength requirements of structural SCC applications. Besides, the heat curing at 45 °C was not efficient to improve the compressive strength compared to the humid curing. The investigated hybrid SCC mixtures exhibited relatively good durability performance reflected by their low chloride ion penetration and good freeze–thaw resistance.

Utilization of Self-Consolidating Concrete Technology for Large Placements in New Nuclear Construction: A Study on Self-Consolidating Concrete Stability and Constructability

Abstract This paper discusses the use of self-consolidating concrete (SCC), in a large-scale placement during new nuclear plant construction. SCC has provided cost and labor savings and construction process improvements. Use of SCC has been effective in schedule acceleration by reducing placement durations and early curing termination with rapid strength gain. Self-consolidating properties were particularly of value at placements of poor access as internal vibrators were not effective and large surface area made form vibrators ineffective beyond the perimeter. This paper provides a discussion of technical challenges encountered in development of a properly functioning SCC mixture, and testing performed to overcome these challenges. The paper discusses the engineering considerations and laboratory and field trials preparing for a 3950 m3 placement for the base of a nuclear plant. The placement was anticipated to take 35 h at 110 m3/h batch plant output. Overview of mix design specifications and mix development is provided. The mixture satisfied the laboratory test parameters including SCC tests; stability and column segregation. However, the mixture had to undergo rounds of constructability testing beyond laboratory development prior to the large placement. Among the constructability properties was the distance SCC will move with the stone before stopping. A long trough was filled as a mockup for and subsequently cored. The number of pumps and pump nozzle placement spacing was determined as a result. Slump flow retention as the polycarboxylate loses effectiveness and foaming of the mixture when pumped were also investigated. Foaming was attributed to viscosity, air entrainer, and pump pressures or rate of pumping. Laboratory trials with various admixtures and pumping studies in the field were conducted to achieve a mixture that retains slump flow and can be pumped at the desired rates without instability or excessive foaming. The placement was completed successfully in 35 h over multiple shifts.

Application of Superabsorbent Polymer as Self-Healing Agent in Self-Consolidating Concrete for Mitigating Precracking Phenomenon at the Rebar–Concrete Interface

Improved autogenous healing capacity of concrete using superabsorbent polymers (SAPs) was used as an efficient approach for mitigating damage between steel rebar and self-consolidating concrete (SCC). The results for normal concrete (NC) and those for SCC mixtures were compared. Two SAPs with different particle sizes and chemical compositions were used in the experimental program. Results showed that despite the greater reduction effect of SAP with a smaller particle size on compressive strength, SCC containing this type of SAP had the highest bond strength in uncracked specimens, compared with SAP with larger particle sizes, for SAP-modified NC and SCC mixtures. Moreover, results showed that SCC and NC containing SAP had considerably greater healing improvement factors for large crack widths (w≥0.30 mm) compared with mixtures without polymers; almost 46%, 30%, and 24% healing improvement factors were obtained for average bond stress, bond strength, and residual bond stress of SAP-containing concrete mixtures, respectively. Furthermore, complete strength recovery (100% healing improvement factor) was obtained for SCC mixture with w=0.10 mm after a 28-day healing period.

New diphasic insight into the restricted flowability and granular blocking of self-consolidating concrete: Effect of morphological characteristics of coarse aggregate on passing ability of SCC

Self-consolidating concrete (SCC) was simulated as a diphasic suspension. The passing ability of SCC was characterized in terms of restricted flowability and granular blocking due to its non-Newtonian behavior and multiphasic nature. New heterogeneity indices were then defined to evaluate the granular blocking-induced variations of relative solid-packing fraction (φ/φmax) of coarse aggregate (>1.25 mm) and, consequently, the rheological properties of SCC in the J-Ring and L-Box set-ups.In total, 30 low- and normal-paste SCC mixtures and their corresponding fine mortar portions (<1.25 mm) were investigated in this study. The passing ability of the investigated SCC mixtures were found in good agreements with the visco-elastoplastic properties and excess volume of fine mortars, as well as the morphological characteristics of coarse aggregate. According to the established correlations, the most effective morphological characteristics and rheological parameters on passing ability of SCC include the mean diameter and roughness of coarse aggregate, as well as the plastic viscosity and yield stress of fine mortar, respectively. On the other hand, a comparative study on the passing ability of SCC in different set-ups revealed that low- and normal-paste SCC mixtures exhibited higher granular blocking indices in the L-Box and J-Ring set-ups, respectively. Furthermore, the robustness and ANOVA analyses showed that optimizing the paste volume, φ/φmax, and morphological characteristics of coarse aggregate is more effective to enhance the passing ability of SCC than adjusting the water-to-binder ratios and high-range water-reducer (HRWR) dosages.

Application of Artificial Intelligence to Evaluate the Fresh Properties of Self-Consolidating Concrete.

This paper numerically investigates the required superplasticizer (SP) demand for self-consolidating concrete (SCC) as a valuable information source to obtain a durable SCC. In this regard, an adaptive neuro-fuzzy inference system (ANFIS) is integrated with three metaheuristic algorithms to evaluate a dataset from non-destructive tests. Hence, five different non-destructive testing methods, including J-ring test, V-funnel test, U-box test, 3 min slump value and 50 min slump (T50) value were performed. Then, three metaheuristic algorithms, namely particle swarm optimization (PSO), ant colony optimization (ACO) and differential evolution optimization (DEO), were considered to predict the SP demand of SCC mixtures. To compare the optimization algorithms, ANFIS parameters were kept constant (clusters = 10, train samples = 70% and test samples = 30%). The metaheuristic parameters were adjusted, and each algorithm was tuned to attain the best performance. In general, it was found that the ANFIS method is a good base to be combined with other optimization algorithms. The results indicated that hybrid algorithms (ANFIS-PSO, ANFIS-DEO and ANFIS-ACO) can be used as reliable prediction methods and considered as an alternative for experimental techniques. In order to perform a reliable analogy of the developed algorithms, three evaluation criteria were employed, including root mean square error (RMSE), Pearson correlation coefficient (r) and determination regression coefficient (R2). As a result, the ANFIS-PSO algorithm represented the most accurate prediction of SP demand with RMSE = 0.0633, r = 0.9387 and R2 = 0.9871 in the testing phase.

How do discharge rate and pipeline length influence the rheological properties of self-consolidating concrete after pumping?

Pumping changes the rheological properties, workability and construction performance of fresh concrete. However, there were limited knowledges on influences of discharge rates and pumping distances on the fresh properties of concrete. In this paper, effects of various discharge rates and pipeline lengths on rheological properties of self-consolidating concrete (SCC) after pumping were studied. A total of 12 SCC mixtures with the slump flow of 650–745 mm were pumped in pipelines with measured lengths of 342 m, 545 m, and 1044 m by constant discharge rates ranging between 5.1 and 11.4 L/s. Rheological properties were measured before and after pumping. Physical conditions of SCC during pumping, including pressure, shear, and temperature were estimated theoretically and experimentally. Moreover, the total organic carbon in the pore solution of SCC mixtures was measured to evaluate the change of superplasticizer adsorptions after pumping. Test results indicated that, due to pumping, the yield stress increased; the initial tangential viscosity decreased and the shear-thickening phenomenon was eliminated. The changes of yield stresses and viscosity were encouraged by discharge rates. Besides, lower initial slump flow of SCC exhibited a larger slump flow loss after pumping due to a higher shear rate experienced during pumping. The yield stress and viscosity after pumping increased with the increase of pipeline length at similar discharge rates, but decreased with the pipeline length under similar pumping pressures. The adsorption of superplasticizer increased after pumped at relative low discharge rates (5.2–5.7 L/s), but decreased at discharge rates of 7.7–10.8 L/s.

Evaluating Prediction Models of Creep and Drying Shrinkage of Self-Consolidating Concrete Containing Supplementary Cementitious Materials/Fillers

Supplementary cementitious materials (SCMs) and fillers play an important role in enhancing the mechanical properties and durability of concrete. SCMs and fillers are commonly used in self-consolidating concrete (SCC) mixtures to also enhance their rheological properties. However, these additives could have significant effects on the viscoelastic properties of concrete. Existing models for predicting creep and drying shrinkage of concrete do not consider the effect of SCM/filler on the predicted values. This study evaluates existing creep and drying shrinkage models, including AASHTO LRFD, ACI209, CEB-FIP MC90-99, B3, and GL2000, for SCC mixtures with different SCMs/fillers. Forty SCC mixtures were proportioned for different cast-in-place bridge components and tested for drying shrinkage. A set of eight SCC mixtures with the highest paste content was tested for creep. Shrinkage and creep test results indicated that AASHTO LRFD provides better creep prediction than the other models for SCC with different SCMs/fillers. Although all models underestimate drying shrinkage of SCC with different SCMs/fillers, the GL2000, CEB-FIP MC90-99, and ACI 209 models provide better prediction than AASHTO LRFD and B3 models. Additionally, SCC mixtures with limestone powder filler exhibited the highest creep, while those with class C fly ash exhibited the highest drying shrinkage.

Form pressure characteristics of self-consolidating concrete used in repair

This paper aims at assessing the lateral pressure exerted by self-consolidating concrete (SCC) on single-sided vertical formwork during repair work. Reinforced concrete repair wall elements measuring 5.6 ± 0.3 m in height and 180 mm in width were cast using SCC mixtures having different thixotropic characteristics at casting rates varying from 6 to 9.5 m/h. Results showed that the actual field pressure values are substantially lower than the equivalent hydrostatic pressure, varying from 60% to as low as 34% at the end of casting. This was attributed to the SCC structural build-up coupled with the presence of vertical/transverse reinforcing bars, arching effect in confined and tall repair sections, and increased friction between the concrete and existing repair substrate. The use of a 1.1-m high experimental PVC column was found appropriate to mimic the decay of lateral pressure observed in the repair wall elements, making it relevant to predict the effect of concrete restructuring on casting rate. Such data can be of interest to tailor the mixture proportions and enhance safety aspects related to casting slender repair sections with SCC.