Self-consolidating Concrete Mixtures Research Articles

Characterisation of damage due to abrasion in SCC by acoustic emission analysis

This investigation evaluates and compares the abrasion resistance of various concrete types by means of acoustic emission (AE) analysis. Normal concrete, self-consolidating concrete (SCC) and SCC with variable supplementary cementing materials (SCMs) were tested under the rotating cutter method for abrasion resistance. The effect of using different SCMs in SCC mixtures including fly ash, metakaolin (MK), silica fume and slag on the abrasion resistance of SCC was examined. In conjunction with the abrasion testing, AE monitoring was simultaneously conducted on all mixtures using AE attached sensors. AE parameters such as signal amplitude, signal strength, number of hits, duration and cumulative signal strength (CSS) were collected during the abrasion tests. Three additional parameters were determined through further analyses: b-value, severity (Sr) and historic index (H(t)). Results from the abrasion tests indicated that the SCC mixture containing MK had the highest abrasion resistance among all tested mixtures. The studied AE parameters including CSS, number of hits, b-value, H(t) and Sr were well correlated to the extent of abrasion damage in all tested specimens. The progression of abrasion damage was associated with increased AE activities indicated by high fluctuations in the b-value and H(t) along with ever-increasing values of CSS, number of hits and Sr. The AE intensity analysis quantified which ranges for H(t) and Sr would indicate the extent and severity of the damage due to abrasion by means of developed damage classification charts.

Toward the prediction of rheological properties of self-consolidating concrete as diphasic material

Understanding the rheology of self-consolidating concrete (SCC) is a key step to ensuring proper flow and successful casting in formworks, and hence good performance of the hardened material. The rheology of SCC is a function of several mixture parameters, including water-to-binder ratio (W/B), paste content, coarse aggregate content and grading, and presence of chemical admixtures. The mix design of SCC is less robust than conventional concrete and necessitates vigorous optimization to ensure adequate flow performance. The research emphasis in this study is on developing a practical approach that can be used to predict rheological properties of SCC as a diphasic material, which will contribute significantly to simplifying the protocols for mixture optimization and material selection. Various SCCs and their corresponding mortar mixtures were investigated covering a wide range of mixture proportion parameters, including W/B, paste-to-sand volume (VP/VS), and coarse aggregate (CA) type and content. The rheological properties of SCC, mortar phases, and the relationship between the two phases are evaluated and discussed in this paper. Test results show very good correlation between the rheological properties of modified design mortar, sieved mortar, and SCC mixtures. Prediction adequacy was mostly affected by VP/VS and W/B parameters. Modified Krieger–Dougherty (KD) and Chateau–Ovarlez–Trung (COT) models satisfactorily predicted the rheological properties of SCC mixtures.

Effect of structural buildup at rest of self-consolidating concrete on mechanical and transport properties of multilayer casting

Multilayer casting of self-consolidating concrete (SCC) can be critical in situations involving delays between the placements of successive lifts. In the absence of mechanical consolidation, the increase in structural buildup at rest (SBR) of existing SCC lift prior to the placement of a successive lift can lead to lift lines. Furthermore, the bond strength deteriorates across the bonded interphases. In this study, eight SCC mixtures with different levels of SBR were considered. The thixotropy of concrete was determined using standard workability test methods and inclined plane test. Flexural strength and water permeability were determined using composite specimens cast in two SCC lifts. The second lift was placed after given periods of rest up to 60 min. Composite specimens developed residual flexural strengths and water permeability resistance with minimum values of 56% and 2%, respectively, compared to reference samples. To secure 90% residual flexural strength and impermeability, delays up to 25 and 10 min can be tolerated, respectively, depending on SBR level of the existing SCC layer. Statistical models were established to predict the residual flexural strength and water permeability resistance between successive lifts. SCC with low level of SBR, having static yield stress up to 250 Pa after 15 min of rest and rate of SBR up to 2.5 Pa/min evaluated using the inclined plane test, can secure relatively high level of bond strength and impermeability providing that the delay time before casting successive lifts is limited to 20 and 5 min, respectively. The interphases bond of successive SCC lifts was found to be affected by intermixing level of the layers. Both can be increased by the reduction in SBR of existing lift when concrete is cast with a given free fall height.

Predicting the Formwork Lateral Pressure of Self-consolidating Concrete Based on Experimental Thixotropy Values

Self-consolidating concrete (SCC), despite its many positive advantages, increases the formwork lateral pressure of the mixture due to its high fluidity, leading to the increased cost of formwork construction in the in situ concrete structures. The thixotropy property, as the most significant functional feature including the effect of mixture proportions on lateral pressure, was selected to investigate the behavior of fresh concrete in the mold. In the present study, the thixotropy and formwork pressure characteristics (including maximum lateral pressure and pressure drop rate) of 15 SCC mixtures were investigated by considering a number of mixtures proportions variables including cement content, water-to-cement ratio, and mineral admixtures. In addition to studying the effect of these variables on the thixotropy level and the lateral pressure of the formwork, the relationship between the methods of measuring the thixotropy level (hysteresis methods, the area of structural breakdown, and the yield stress growth rate) was evaluated considering the mechanism of these methods. In this study, formwork pressure simulator device was used to measure maximum lateral pressure and lateral pressure drop rate. In addition, the effects of mixture proportioning variables on thixotropy and its relationship with the formwork pressure were studied. Using these indices, the ability to predict the behavior of concrete in the mold was investigated through modeling. The presented predicting model of the formwork pressure based on thixotropy value showed an acceptable correlation coefficient (R2 > 0.77).

Feasibility of using cellulose filaments as a viscosity modifying agent in self-consolidating concrete

Nanomodification of concrete represents one of the phenomenal leaps in concrete technology providing innovative tools for engineering cement composites with improved performance. In self-consolidating concrete (SCC), for instance, designing flowable–yet stable and robust–SCC mixtures requires an optimum balance between flowability and stability. This is conventionally achieved by optimizing the dosage of high range water reducing admixtures (HRWRA) indispensable for flowability, while increasing the binder content or introducing viscosity modifying agents (VMA) necessary for stability. This study shows how cellulose filaments (CF)–a new type of nanocellulose materials–can be used as a novel tool for rheology modification and strength enhancement in SCC. CF were incorporated at concentrations ranging from 0.05 to 0.30% per weight of binder in cement pastes and SCC. Rheological and mechanical properties of CF systems were compared to those of plain systems and systems incorporating a commercially available VMA of welan gum type. Results showed that CF serve as a VMA due to the buildup of flexible nanoscale CF networks. As such, a geometry-based percolation model showed that at a concentration of 0.12 wt.%, a network of percolating CF was formed. Beyond this CF content, the yield stress, the plastic viscosity, as well as the HRWRA demand exhibited a substantial increase. CF networks increased mixture viscosity–essential for stability–at low shear rates. On the other hand, at high shear rates, CF networks led to lower apparent viscosity essential for improving pumpability; owing to the streamlining of the flexible nanocellulose fibrils in the direction of flow, thereby imparting a shear thinning behavior. Furthermore, CF imparted improvement in mechanical performance of 12–26% in compression, splitting-tension, and flexure. Research outcomes are expected to contribute towards offering an alternative VMA with strength improvement potential while contributing towards the implementation of sustainable materials for concrete technology.

Assessing abrasion performance of self-consolidating concrete containing synthetic fibers using acoustic emission analysis

The key objective of this investigation was to evaluate the abrasion resistance of self-consolidating concrete (SCC) with and without synthetic fibers (SynFs). The abrasion resistance of normal concrete was also investigated in this study for comparison. The abrasion test was performed on concrete specimens according to the rotating-cutter method along with continuous monitoring of acoustic emission (AE) using attached AE sensors. The effects of changing concrete type and incorporating various types (flexible and semi-rigid) and lengths of SynFs on the abrasion behaviour were investigated with the aid of AE analysis. AE signal characteristics such as amplitude, signal strength, number of hits, and duration were gathered during testing. Furthermore, the collected AE data was used to complete b-value analysis as well as intensity analysis resulting in three additional parameters: b-value, severity (Sr), and historic index (H(t)). The results showed that the AE parameters were directly correlated with the abrasion damage in all tested mixtures. Adding SynFs to all SCC mixtures enhanced their abrasion resistance. The flexible fibers variety exhibited better abrasion performance on average than the semi-rigid fibers. Meanwhile, longer fibers showed lower abrasion resistance than the shorter ones with the same type. The results also indicated that AE intensity analysis was able to determine the ranges for H(t) and Sr that identify the extent of damage due to abrasion of SynF-reinforced SCC.

Regression models to predict SCC pressure exerted on formworks containing vertical and transverse reinforcing bars

The use of self-consolidating concrete (SCC) containing recycled concrete aggregate (RCA) considerably increased in sustainable structural applications and civil engineering works. However, current literature and construction practices are not clear regarding the influence of RCA additions and presence of steel reinforcement on formwork pressure exerted by the plastic concrete. This paper reports experimental data obtained from 32 SCC mixtures possessing different stability levels and cast in 1.6-m high formwork containing various combinations of vertical and transverse steel bars. Test results have shown that mixtures incorporating recycled aggregates exhibited reduced initial maximum pressure, given the higher RCA surface roughness that promotes internal friction and material build-up at rest. The decrease in pressure was particularly accentuated in presence of steel bars, suggesting that the reinforcement cage confines the plastic concrete and carries part of its load. The transverse steel was around 1.5-times more influential than vertical steel in reducing the formwork pressure. The rates of pressure drop over time were not altered because of steel, implying that pressure decay is governed by the concrete intrinsic properties such as thixotropy, RCA friction, and cement hydration. Special emphasis was placed to develop regression models and examine suitability of existing ones to predict lateral pressure of RCA-modified SCC cast in formworks containing reinforcing bars.

Influence of thixotropy determined by different test methods on formwork pressure of self-consolidating concrete

In this experimental study, the influence of thixotropy determined by different test methods on the formwork pressure of self-consolidating concrete (SCC) with varying compositions was investigated. In order to determine the effect of water/binder (w/b) ratio, slump flow diameter and coarse aggregate/total aggregate (CA/TA) ratio on thixotropy and formwork pressure of SCC, fifteen concrete mixtures were prepared. Four different test methods i.e., “structural break-down area” (SBDA), “break-down percentage” (BDP), “drop in apparent viscosity” (DAV) and “yield value at rest” (YVR) were performed to determine the thixotropy of the SCC mixtures. Test results showed that the SBDA, DAV and YVR methods were more appropriate to evaluate the thixotropy of SCC than the BDP method. A strong correlation between thixotropy and formwork pressure was found using SBDA, DAV and YVR methods in SCC mixtures having low w/b ratio. There was a strong relationship between thixotropy determined by SBDA, BDP and DAV methods and formwork pressure in low slump flow SCC mixtures, while thixotropy determined by the YVR method showed good correlation with the formwork pressure in SCC mixtures having high slump flow values. Finally, new models were developed to estimate the formwork pressure of all kinds of mixtures as a function of thixotropy and time. The models were found to be successful for each of the thixotropy measurement method.

A new method for determination of dynamic stability of self-consolidating concrete: 3-Compartment sieve test

There are many standard test methods and applications to determine or estimate the workability of fresh concrete mixtures, most of them are focused on highly flowable concrete mixtures. Due to its high flowability, self-consolidating concrete (SCC) is much more vulnerable to segregation compared to conventional concrete mixtures. Thus, researchers have been working on adopting dynamic and static test methods for determination and improvement of segregation stability of those mixtures. In this study, the different segregation test methods presented in the literature were assessed and a novel method, i.e. 3-compartment sieve test, was introduced. The dynamic stability of fresh self-consolidating concrete mixtures was evaluated by the suggested test method after slump-flow and J-Ring tests. In conclusion, the developed new method is recommended for determination of segregation in SCC due to satisfactory concurrency of results with those of visual stability index test (0.67 ≤ R2 ≤ 0.90) and sieve segregation resistance test (0.83 ≤ R2 ≤ 0.90), respectively.

Reducing variations in the test results of self-consolidating lightweight concrete by incorporating pozzolanic materials

Portland limestone cement (PLC) has been considered as a suitable alternative for portland cement in self-consolidating lightweight concrete (SCLWC) mixtures. However, certain inconsistencies were reported in terms of strength development and durability properties of the PLC concrete. In addition, fresh SCLWC mixtures are more likely to encounter test results variation than ordinary concrete mixtures. This paper experimentally investigates the fresh and hardened performance of SCLWC incorporating ternary blended cements containing PLC and silica fume (SF), fly ash (FA), natural zeolite (ZE) or metakaolin (MK). The fresh tests were repeated once for each 100-L concrete batch and coefficient of variation as a measure of dispersion of a frequency distribution used to determine the variation of fresh test results of the mixtures. The results show that the pozzolanic materials mixtures have greater but less variable results of flowability compared to the PLC mixture. The coefficient of variation in results of slump flow test is varied 0.8–2.9%. It was also observed that there is a reduction in variation of the V-funnel results as the mean value increased. The obtained coefficient of variation was as low as 7% for zeolite ternary mixtures and the highest variation belonged to the binary mixture by 19.2%. The result of rapid chloride migration test (RCMT) and electrical resistance test indicated that there is a strong correlation between these two variables. Comparing the results to other studies, we recognized that the correlation seems to be unique for each case study.

Effect of GGBS on the frost resistance of self-consolidating concrete

Frost resistance of self-consolidating concrete (SCC) is very important in structures exposed to cold weather. On the other hand, Ground granulated blast-furnace slag (GGBS) as a waste material of industries can be replaced by cement in order to reduce cost of concrete production and also decreases the environmental Pollution. In this study, freeze-thaw resistance of SCC mixture prepared with w/c ratio of 0.44 and having cement as 418 kg/m3 was investigated in accordance with ASTM C 666 standard. In These Experiments Cement is replaced with 0%, 30%, 50%, 65% and 80% GGBS. Another SCC mixtures combining 50% GGBS with 5%, 10% and 15% silica fume were tested for Freezing-thawing resistance evaluation. Results of Experiments have shown that the more GGBS replaced with Cement, the lower frost resistance concrete has. It is also seen that increasing GGBS percentage in SCC reduces Compressive strength.

Evaluation of laboratory performance of self-consolidating concrete with recycled tire rubber

Abstract This study investigated the performance of early-aged and hardened self-consolidating concrete (SCC). Rubber-modified SCC mixtures were prepared with 15% as-received crumb rubber and 15% and 25% NaOH-treated crumb rubber based on volume of fine aggregates. The SCC sampled without rubber aggregates were cast as the control groups. The slump test, V-flannel flow test, and U-box test were conducted to evaluate the fresh properties of different types of rubber modified SCC. The fresh properties showed slightly reduced flowability with replaced rubber particles. The measured compressive and splitting tensile strength of rubber-modified SCC concrete were reduced in comparison with the control mixture. However, the surface-treated rubberized concrete had higher mechanical strength than as-received rubberized concrete due to better bonding at the interface. The measured ultrasonic transmission speed decreased with the increasing rubber content in concrete and these results also indicated the reduced dynamic modulus. The transport property evaluated from the electrical resistivity measurement indicated the decreased permeability with added rubber content. The durability performances (including alkali-silica reaction and drying shrinkage) of SCC mortar samples were generally improved with rubber-modified samples. Overall study showed that the rubber-modified SCC can maintain good workability and mechanical properties and enhance durability with reduced environmental impacts.

Key mechanical properties and microstructure of carbon fibre reinforced self-consolidating concrete

This paper presents the key mechanical properties and microstructure of different carbon fibre reinforced self-consolidating concrete (CFRSCC) mixtures. Two different water-to-binder (W/B) ratios of 0.35 and 0.40 were used to produce ten CFRSCC mixtures including 0–1% carbon fibres by volume of concrete. The key mechanical properties such as compressive strength, splitting tensile strength, flexural strength or modulus of rapture, and toughness or fracture energy of CFRSCCs were determined. In addition, the load-deflection behaviour was studied for all CFRSCCs. The microstructure of all CFRSCCs was also observed via scanning electron micrographs (SEMs) of the fracture surface to examine the distribution and failure mode of carbon fibres in self-consolidating concrete. Test results revealed that the increased amount of carbon fibres decreased the compressive strength of CFRSCC by 36.6–58.9% depending on W/B ratio and curing age. However, the higher amount of carbon fibres increased the splitting tensile strength of CFRSCC by 13.1–17% at different W/B ratios and curing ages. Also, the flexural strength and toughness of CFRSCC was increased by 3.6% and 41.4%, respectively, for 0.25% carbon fibres. The load-deflection behaviour diagrams showed that the CFRSCC with 0.25% carbon fibres had the best post-peak response under loading. Furthermore, the SEMs exhibited that the CFRSCCs with 0.35 W/B ratio were denser with lesser pores than the CFRSCCs with 0.50 W/B ratio. Carbon fibres were well-distributed in concrete when the fibre content was 0.25%. It was also observed from SEMs that carbon fibres failed either by pullout or breakage under loading.

The combined effect of crumb rubber and synthetic fibers on impact resistance of self-consolidating concrete

This study was conducted to evaluate the impact resistance and mechanical properties of self-consolidating rubberized concrete (SCRC) mixtures reinforced with synthetic fibers (SFs). In particular, the investigation aimed to maximize the impact resistance and energy absorption of SCRC mixtures by optimizing the mixture proportions and by using the most appropriate types and volumes of SFs. The study also presented the effect of steel fibers (SLFs) on the impact resistance and mechanical properties of SCRC for comparison. The tested fibers consisted of three types of flexible SFs (19-mm, 38-mm, and 50-mm), two types of semi-rigid SFs (27-mm and 54-mm), and two types of hooked-end SLFs (35-mm and 60-mm). The results indicated that increasing the CR content had a negative effect on the mechanical properties of SCRC mixtures, while the ductility and impact resistance were significantly improved. Using SFs in SCRC mixtures further increased the impact resistance and appeared to alleviate the reduction in splitting tensile strength (STS) and flexural strength (FS) that resulted from adding CR. Although using longer SFs had a negative impact on the fresh properties of SCRC, it greatly improved the mechanical properties and impact resistance of the mixtures. The results also indicated that in the absence of the challenge of achieving self-compactibility, it was possible to develop vibrated rubberized concrete with higher percentages of CR and SFs, which in turn resulted in higher improvements in STS, FS, impact resistance, and further reduction in the self-weight of concrete.

Development of self-consolidating rubberized concrete incorporating silica fume

This investigation was carried out to evaluate the effect of using silica fume on the development and optimization of self-consolidating rubberized concrete (SCRC). In particular, the investigation aimed to optimize successful silica fume self-consolidating rubberized concrete (SLFSCRC) mixtures with maximized percentage of crumb rubber (CR) (as a partial replacement of fine aggregate) and minimized strength reduction. The study also compared the behaviour of silica fume (SLF) with other supplementary cementitious materials (SCMs) in optimized SCRC mixtures. The results indicated that the use of SLF helped to develop SCRC mixtures with improved strength and acceptable fresh properties with up to 25% CR. Using SLF or metakaolin (MK) in SCRC exhibited superior behaviour among other SCMs in terms of strength. However, using SLF in SCRC showed better mixture flowability and less dosage of high range of water reducer admixture compared to using MK in SCRC. It was also noticed that adding steel fibres (SFs) to SLFSCRC mixtures greatly enhanced the mechanical properties, especially the splitting tensile strength and flexural strength. The results also showed that since there is no challenge to achieving acceptable self-compactibility (especially passing ability) in vibrated rubberized concrete, it was possible to develop silica fume vibrated rubberized concrete (SLFVRC) with higher percentages of CR and SFs and with further improved flexural and tensile strengths.

Effects of calcium carbonate powder on the fresh and hardened properties of self-consolidating concrete incorporating untreated rice husk ash

In this paper, the effects of calcium carbonate powder on the properties of self-consolidating concrete (SCC) incorporated with untreated rice husk ash (RHA) and calcium carbonate powder (CC) are presented. CC was utilized as an ordinary Portland cement (OPC) substitute at percentage replacements of 20% and 40% by weight, and RHA was used as a fine aggregate replacement material at a percentage replacement of 20% by weight. The SCC mixtures were designed with a controlled slump flow of 725 ± 25 mm. The properties in the fresh and hardened states of the blends of OPC and CC were investigated using the slump flow time, V-funnel flow time, flow diameter from the J-ring test, compressive strength, and resistance to sulfuric acid attack. The results showed that the use of CC can reduce the water content of the powder materials (OPC + CC). Remarkably, the resulting concretes maintained their slump flow and could flow through a V-shaped box and the obstacles used to assess the J-ring test, thus satisfying the criterion declared by European Federation of Producers and Applicators of Specialist Products for Structures (EFNARC). Moreover, the highest compressive strength was achieved in the SCC mixture with 20% CC1 (Dv, 50 = 3.95 μm). Compared with SCC without RHA, the addition of RHA requires an increased ratio of water/powder (w/p) materials (OPC + CC). Furthermore, in the case of concrete without RHA, the SCC containing CC exhibited a lower weight loss after sulfuric acid (H2SO4) attack than the control SCC.

Rheology of self-consolidating concrete in hot weather conditions

The rheological properties of fresh concretes incorporating various supplementary cementitious materials (SCMs) in binary and ternary blends were investigated as a function of mixing time, temperature and SCM dosage. Two types of SCMs were tested: silica fume and fly ash. Ordinary Portland cement concrete mixtures were designed with a constant water to cementitious materials ratio of 0·36 and incorporating a fixed dosage of polycarboxylate-based high-range water-reducing admixture. Self-consolidating concrete (SCC) mixtures were continuously mixed for up to 110 min using a drum mixer at different ambient temperatures (25, 30, 35 and 40°C). Rheological testing was performed using a BT2-type concrete rheometer. The relative yield stress was found to have an exponential correlation with the slump flow. The relationship between the relative yield stress and relative viscosity was investigated. The aim of this study was to gain understanding into the contribution of SCM type and dosage to mitigate the harsh effects of hot temperature and prolonged mixing on the rheology of green SCC mixtures. The findings of this study are of practical significance that can provide realistic recommendations on the use of SCMs in hot weather conditions.

Automatic image analysis process to appraise segregation resistance of self-consolidating concrete

The segregation of coarse aggregate in self-consolidating concrete (SCC) can result in some defects in the long-term properties of concrete. In this study, an image processing algorithm has been proposed and implemented, using standard coding languages, to assess segregation of the SCC mixtures. This algorithm has been designed to evaluate the distribution of coarse aggregate and the average thickness of the mortar band layer of SCC. Seven mixtures containing fly ash and silica fume as partial replacements for cement were analysed. Slump, J-ring flow and compressive strength of the samples were also measured. The results revealed that an increase in fly ash replacement resulted in a higher segregation index and a higher ratio of mortar band thickness. However, substitution of silica fume caused a lower segregation index and a lower ratio of mortar band thickness. The results demonstrate that there is a high degree of correlation between the segregation index and the mortar band thickness in all the mixtures.

Effect of vertical reinforcing bars on formwork pressure of SCC containing recycled aggregates

The feasibility of self-consolidating concrete (SCC) containing recycled concrete aggregate (RCA) was demonstrated in structural civil engineering applications. Yet, limited information exists regarding the effect of RCA additions, especially in presence of steel reinforcement, on lateral pressure exerted on formworks. This paper reports experimental data obtained from twenty-one SCC mixtures cast in 200 × 400 × 1600-mm formwork containing up to 4.71% vertical steel (the spacing between transverse steel was set to 450mm). Test results have shown that mixtures incorporating RCA exhibited reduced initial pressure, which was mostly attributed to higher aggregate surface roughness that increases internal friction. The decrease in pressure was accentuated with the increase in vertical steel density, suggesting that the reinforcement cage confines the plastic concrete and carries part of its load. Special emphasis was placed to develop conservative reinforcement indices for appropriate prediction of SCC pressure, as well as propose modifications for existing models to account for the effect of RCA additions and presence of vertical steel bars.

Use of Steel Fibers to Optimize Self-Consolidating Concrete Mixtures Containing Crumb Rubber

Use of Steel Fibers to Optimize Self-Consolidating Concrete Mixtures Containing Crumb Rubber