Self-consolidating Concrete Mixtures Research Articles

Repeatability of Workability Test Methods of Self-Consolidating Concrete

In general, in the evaluation of a test method, the repeatability tests must be performed to establish upper and lower bounds for the precision of a test method. The repeatability is calculated as a standard deviation and relative error of test results. In order to evaluate the repeatability of the workability tests used in self-consolidating concrete (SCC) applications, an SCC mixture proportioned with 0.38 w/cm, Type MS cement, 480 kg/m3 of binder , and crushed aggregate with MSA of 12.5 mm was used. The dosage rate of the HRWRA of the SCC was adjusted to secure two initial slump flow consistency levels of 630 ± 10 mm and 700 ± 10 mm for the repeatability tests. For each consistency level, the concrete was batched five times (for a total of 10 mixtures). Each test was repeated five times by the same operator in order to establish the single-operator precision values. Furthermore, five different operators were used to perform each of the workability tests in order to assess the multi-operator error that could occur during testing. Based on the relative errors obtained in the repeatability tests, relatively low error values were obtained for the slump flow, J-Ring flow, and L-box blocking ratio tests. Relative errors for recommended SCC workability test methods were also summarized.

Use of spent foundry sand and fly ash for the development of green self-consolidating concrete

In the United States alone, the foundry industry discards up to 10 million tons of sand each year, offering up a plentiful potential resource to replace sand in concrete products. However, because the use of spent foundry sand (SFS) is currently very limited in the concrete industry, this study investigates whether SFS can successfully be used as a sand replacement material in cost-effective, green, self-consolidating concrete (SCC). In the study, SCC mixtures were developed to be even more inexpensive and environmentally friendly by incorporating Portland cement with fly ash (FA). Tests done on SCC mixtures to determine fresh properties (slump flow diameter, slump flow time, V-funnel flow time, yield stress, and relative viscosity), compressive strength, drying shrinkage and transport properties (rapid chloride permeability and volume of permeable pores) show that replacing up to 100% of sand with SFS and up to 70% Portland cement with FA enables the manufacture of green, lower cost SCC mixtures with proper fresh, mechanical and durability properties. The beneficial effects of FA compensate for some possible detrimental effects of SFS.

Shrinkage of Full-Scale Girders Cast with Self-Consolidating Concrete

Shrinkage can be critical factor for the design of structural members due to the length changes by the time-dependent deformation. In this investigation, two self-consolidating concrete (SCC) and two high-performance concrete (HPC) mixtures with target 56-day compressive strengths of 55 and 69 MPa and having 18-hour release strengths of 34.5 MPa and 43 MPa, respectively, were used to cast four full-scale AASHTO-Type II girders measuring 9.44-m in length. For each strength level, the SCC and HPC mixtures were proportioned with the same water-to-cementitious materials ratio (w/cm) and binder type. The high-range water-reducing admixture (HRWRA) dosage was adjusted to obtain a slump flow of 680 ± 20 mm for the SCC mixtures and a slump of 160 ± 20 mm for the HPC mixtures. The constructability and shrinkage of full-scale girders cast with SCC and HPC mixtures used in precast prestressed girders were investigated and compared. Results of tests on full-scale girders indicated that, SCC placement was successfully carried out by casting the concrete from location at the midspan of the 9.44-m long girders. Both HPC and SCC mixtures developed similar autogenous shrinkage for the mixtures made with the similar w/cm; the two SCC mixtures developed about 20% greater drying shrinkage than the comparable HPC mixtures after 112 days of drying.

Shear Characteristics and Design for High-Strength Self-Consolidating Concrete

To achieve adequate flow and homogeneous concrete for precast, prestressed members, self-consolidating concrete (SCC) typically has higher paste and lower coarse aggregate volumes than conventional concrete (CC). The lower aggregate content of SCC can affect the shear capacity of concrete systems. This research performed 48 push-off tests to investigate the influence of SCC aggregate and paste volumes on the shear capacity and these results were compared with those obtained from similar CC samples. The variables included coarse aggregate type (river gravel and limestone), three coarse aggregate volumes for the SCC mixtures, and two target 16-h release strengths [34 and 48 MPa (5 and 7 ksi)]. The aggregate type, aggregate volume, and concrete strength were found to have significant effects on the aggregate interlock. Test results were used to propose new aggregate interlock models based on the modified compression field theory adopted in the AASHTO Load and Resistance Factor Design Specifications. More appropriate expressions have been developed to determine the limiting value of concrete shear strength for CC and SCC precast, prestressed concrete girders with similar mixture proportions, and a 28-day compressive strength greater than 70 MPa (10 ksi).

Comparison of Workability Test Methods for Self-Consolidating Concrete

Abstract Data from two research projects were analyzed to evaluate the suitability of seven empirical workability test methods for self-consolidating concrete (SCC)—namely, the column segregation test, J-ring test, L-box test, penetration apparatus test, sieve stability test, slump flow test, and V-funnel test. The results of these empirical tests were compared to rheometer measurements. Test methods were evaluated based on (1) the extent to which each method independently indicated filling ability, passing ability, or segregation resistance and (2) the ease and simplicity with which each test method can be used on a routine basis in the laboratory or the field. The data set consisted of 286 SCC mixtures incorporating a range of materials, mixture proportions, and workability characteristics. It was determined that the slump flow test should be used for filling ability, the J-ring test for passing ability, and the column segregation test or sieve stability test for segregation resistance.

Characterization of High Early-Strength, Self-Consolidating Concrete for Design of Pretensioned Bridge Elements

Self-consolidating concrete (SCC) is an innovative construction material that can be placed into forms without mechanical vibration. Precast, prestressed concrete plants require that the concrete used to fabricate their structural members attain high early strength. High early-strength SCC could provide significant value for precast plants. However, the high early-strength SCC mixture constituents, proportions, and construction may affect the hardened properties, and SCC may not provide the same performance as conventional concrete. SCC and conventional concrete mixture proportions designed for precast, prestressed bridge elements were evaluated to characterize the associated mechanical properties, shear characteristics, bond characteristics, and creep. To assess the applicability of SCC in prestressed girder systems, four full-scale girder–deck systems containing conventional concrete and SCC precast girders were fabricated and tested. Results from this research indicate that the AASHTO Load and Resistance Factor Design Specifications can be used to estimate the mechanical properties of high early-strength SCC. With respect to shear characteristics, a more appropriate expression is proposed to estimate the concrete shear strength for SCC girders with a compressive strength greater than 10 ksi (69 MPa). Bridge girder–deck systems containing relatively small (Texas Type A) girders containing high early-strength SCC exhibited similar flexural performance as bridge girder–deck systems with girders containing conventional concrete. Results indicate that the AASHTO equations for computing the nominal moment capacity, strand transfer length, and strand development length may be used for SCC girder–deck systems similar to those tested in this study.

New Methodology to Proportion Self-Consolidating Concrete with High-Volume Fly Ash

This article introduces a new methodology to proportion self-consolidating concrete (SCC) suitable for high-volume ASTM Class F fly ash content. Ingredients are determined from explicit criteria on strength and rheology. The water-cementitious material ratio (w/cm) is derived from the model systematically developed for this study. The quantity of chemical admixture and fine aggregates are determined from the rheological requirement. Finally, the quantity of coarse aggregate is calculated using the absolute volume method and finalized by adjusting the volume fractions. The suitability of the method is examined by proportioning SCC mixtures with different powder composition and fine aggregate types. The workability and compressive strength as well as the split tensile strength of these mixtures are tested. The results suggested that the method was adequate to proportion SCC mixtures with ingredients used in this study, satisfying both of the requirements of strength and rheology.

Bond strength of deformed bars in large reinforced concrete members cast with industrial self-consolidating concrete mixture

The bond strength of reinforcing bars embedded in full-scale heavily reinforced concrete sections made with industrial self-consolidating concrete (SCC) was investigated and compared with that of normal concrete (NC). The flowability of SCC mix through the dense reinforcement was visually monitored from a transparent formwork. The bond stress was tested for bars located at three different heights (150 mm, 510 mm, and 870 mm from the bottom of the pullout specimens) and at different tested ages (1, 3, 7, 14, and 28 days). The bond stress-free end slip relationship, the top bar effect and the effect of age on bond stress was investigated in both SCC and NC pullout specimens. Bond stresses predicted based on some major codes were compared with those obtained from experiments. The results indicated that casting SCC was much faster and easier and could be done with less labor effort and no concrete blockage among the heavy reinforcements compared to NC. The results also indicated that the bond stress was slightly higher in the SCC pullout specimen compared to the NC pullout specimen. The difference was more pronounced in the top bars and at 28 days of testing.

Fresh, Mechanical, and Durability Characteristics of Self-Consolidating Concrete Incorporating Volcanic Ash

Self-consolidating concrete (SCC) is known for its excellent deformability, high resistance to segregation, and use in congested reinforced concrete structures characterized by difficult casting conditions without applying vibration. The use of known mineral admixtures such as fly ash and slag cement has proved very effective in the production of nonexpensive SCC with satisfactory fresh and hardened properties. However, the use of volcanic ash (VA) in SCC is new and can provide low cost SCC. This paper presents fresh, mechanical, and durability characteristics of VA based SCC mixtures (VA-SCCs). VA-SCCs are developed by varying water-to-binder ratio, percentages of VA as cement replacement, and dosages of superplasticizer (SP). Mix design parameters are optimized to achieve minimum use of SP and optimum use of VA. The fresh concrete properties are determined from slump flow, V-funnel flow time, bleeding, air content, and segregation tests. The mechanical properties and durability characteristics such as compressive strength, freezing-thawing resistance, rapid chloride permeability, surface scaling resistance, and drying shrinkage are determined to evaluate the performance of VA-SCCs. The study produces encouraging results and confirms the production of satisfactory VA based SCC mixtures with acceptable properties. VA-SCCs having a minimum strength of 15 MPa (requirement for some structural concrete applications) can be obtained by replacing up to 50% (by mass) of cement by VA. Development of nonexpensive and environmental friendly VA-SCC with acceptable strength and durability characteristics (as illustrated in this study) is extremely helpful for the sustainable development and rehabilitation of volcanic disaster areas around the world.

Self-consolidating concrete subjected to high temperature: Mechanical and physicochemical properties

This paper presents an experimental study on the performance of self-consolidating concrete (SCC) subjected to high temperature. Two SCC mixtures and one vibrated concrete were tested. These concrete mixes were developed in the French National Project B@P. Mechanical and microstructural properties were studied at ambient temperature and after heating. We studied compressive strength, flexural strength, bulk modulus of elasticity, porosity and permeability. For each test, the specimens were heated at a rate of 1 °C/min up to different temperatures (150, 300, 450 and 600 °C). In order to ensure a uniform temperature throughout the specimen, the temperature was held constant at the target temperature for 1 h before cooling. In addition, the specimen mass was measured before and after heating in order to determine the loss of water during the test. The results allowed us to analyze the degradation of SCC and vibrated concretes due to heating.

Use of foundry silica-dust in manufacturing economical self-consolidating concrete

This paper presents results of an experimental work conducted on the use of foundry silica-dust in self-consolidating concrete (SCC). A control SCC mixture was made, in which ASTM C 618 Class C fly ash constituted 40 mass% of the total cementitious materials. Three more SCC mixtures were made using silica-dust obtained from an iron foundry, collected by a high-efficiency baghouse. Silica-dust was used to replace 10%, 20%, and 30% of fly ash at a 1:2 (fly ash to foundry dust) ratio by mass. The extra amount of foundry dust was treated as very fine sand. Use of foundry dust in SCC resulted in high air content (7–10%), possibly due to reaction between foundry dust and the particular chemical admixtures used. With the increase in foundry dust content containing iron, the color of concrete changed to dark gray or black. At 30% replacement of fly ash with foundry silica-dust, the demand for high-range water-reducing admixture (HRWRA) increased. As the foundry dust content increased, the demand for viscosity-modifying admixture (VMA) decreased. It was concluded that foundry silica-dust material could be used in producing economical SCC.

Fuzzy logic approach for estimating durability of concrete

In this work, it is shown how fuzzy inference systems can be constructed to produce a global durability evaluation factor for concrete based on various performance criteria from accelerated tests. This can facilitate the decision-making process during the design stage by identifying optimum concrete mixtures proposed for specified field exposure. A fuzzy inference system was built for the specific case of various self-consolidating concrete mixtures subjected to ammonium sulfate attack. The performance of this model was compared with that of other models that enable decision making: the remaining service life model and compromise programming. Results of the fuzzy inference system had a better correlation with compromise programming (R2 = 0·7) than that with the remaining service life model (R2 = 0·5), and better represented the actual degradation observed in test specimens. It is shown that the proposed fuzzy inference model is rational, clear, reliable, versatile and flexible since it can be easily updated with new data or modified to accommodate future findings.

Effect of mix design on restrained shrinkage of self-consolidating concrete

This paper presents test results carried out to evaluate the potential due to restrained shrinkage cracking of self-consolidating concrete (SCC). The mix design approach and binder type of the SCC are shown to have considerable influence on cracking potential. Mixtures made with 0.42 w/cm and incorporating viscosity-enhancing admixture (VEA) to ensure proper stability exhibited approximately 25–35% longer time before cracking than SCC prepared with 0.35 w/cm and no VEA. The former concrete design had lower elastic modulus at 3 days when the drying shrinkage was initiated and hence greater stress relaxation. This was reflected in greater tensile creep coefficient which reduces tensile stress due to restrained shrinkage. The SCC made with 0.42 w/cm exhibited slightly higher drying shrinkage after 56 days of drying compared to similar concrete prepared with 0.35 w/cm. In general, the tested SCC mixtures had higher cracking potential than the reference high-performance and conventional concretes. This may be due to the higher paste volume of SCC that resulted in greater drying shrinkage. Mixtures with 670 mm slump flow consistency and 180 mm slump values of the same mix design had similar elapsed times before cracking of 6.3 and 5.6 days, respectively.

Durability of self-consolidating concrete to sulfate attack under combined cyclic environments and flexural loading

Classical sulfate immersion tests for concrete have often given different behaviour from that observed in real field exposure. Such tests do not consider other parameters existing in service that can affect the mechanisms and kinetics of sulfate attack. On the other hand, the current shift towards performance-based standards and specifications for concrete requires the development of performance tests that better correlate to field conditions. Such holistic tests can effectively evaluate the service life of normal and emerging types of concrete. With the growing use of self-consolidating concrete (SCC) in various infrastructure applications, it has become necessary to establish reliable data on its durability. In the present study, the durability of a wide range of SCC mixture designs to sulfate attack is assessed when other concomitant damage mechanisms (cyclic environmental conditions and flexural loading) are considered. Based on the tested mixture design variables (type of binders, air-entrainment, sand-to-total aggregates mass ratio, and hybrid fibre reinforcement), potential performance risks (in terms of physico-mechanical parameters) under such a combined exposure were identified. Those risks were not tangible under a full-immersion test method. Thermal, mineralogical and microscopy analyses revealed the coexistence of complex deterioration processes in SCC under the combined exposure, which is fundamentally different from the occurrence of a single damage mechanism (sulfate attack).

Transport Properties of Self-Consolidating Concrete

This study reports the findings from an investigation carried out to study the effect of the mixture variations on the durability of medium- and high-strength self-consolidating concrete (SCC). The mixture variations studied include the type of mineral admixtures, such as limestone powder (LSP) and pulverized fuel ash (PFA), and viscosity-modifying admixtures (VMA) for both medium- and high-strength SCC. Air permeability, water permeability, capillary absorption, and chloride diffusivity were used to assess the durability of SCC mixtures in comparison with normal, vibrated concretes. The results showed that SCC mixtures, for medium- and high-strength grades using PFA followed by LSP give lower permeability, properties compared with normal concretes. SCC made with VMA had a higher sorptivity, air permeability, and water permeability compared with other SCC mixtures, which can be attributed to higher water-cement ratio (w/c) and lack of pore filling effect. An in-place migration coefficient was obtained using the in-place ion migration test. This was used to compare the potential diffusivity of different concretes. The results indicated that SCC, for both grades of strength, made with PFA showed much lower diffusivity values in comparison with other mixtures, whereas the SCC mixtures with VMA showed higher diffusivity.

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.

Self-Consolidating Concrete Robustness in Continuous Production Regarding Fresh and Hardened State Properties

Due to its advantages over conventional concrete, there has been a considerable increase worldwide in the number of applications using self-consolidating concrete (SCC). Engineers have been encouraged to study the stability of different SCC mixture designs in terms of robustness further because of good degrees of reliability associated with large-scale SCC production. SCC mixture robustness is its properties' stability when errors affect original mixture design in weighing the constituents. Six different SCC mixture designs were selected for SCC robustness evaluation. After they were applied with variations, large scale production errors were simulated, and there was evaluation of their properties in fresh and hardened states. Analysis of variance was used to analyze how such errors influenced concrete properties. Additionally, there was comparison of statistical distributions of real data errors obtained from several Spanish concrete producers and tolerances generally accepted by codes. Traditional concrete tolerances generally have also proven to be valid for SCC. Water and fines content weighing errors are admissible up to ±6% and are of capital importance.

Behavior of Columns Constructed with Fibers and Self-Consolidating Concrete

Steel fiber reinforced concrete was first developed in the 1960s, but the use of this material in load-carrying structural elements has not yet gained wide acceptance. This paper describes a series of 13 full-scale axial compression tests that was conducted on reinforced concrete (RC) and steel fiber-reinforced concrete (SFRC) columns. The objectives were to gain a better understanding of the performance enhancements that can be gained from the use of SFRC in columns and to examine if the provision of fibers would permit a reduction of confinement reinforcement. The specimens, which were detailed with varying amounts of transverse reinforcement, were cast using self-consolidating concrete (SCC) that contained various quantities of fibers. The results demonstrate that the addition of fibers leads to improved load-carrying capacity and post-peak response, and greatly delays cover spalling. The findings also show that the addition of steel fibers can partially substitute for the confinement reinforcement in columns, thereby improving constructability while achieving significant confinement. Although an addition of moderate amount of fibers to SCC can result in an adequately workable concrete mixture, there is a limiting fiber content above which the SCC mixture can lose much of its workability.

Long-Term Deflection of Reinforced Self-Consolidating Concrete Beams

The long-term behavior of reinforced self-consolidating concrete (SCC) beams has been investigated. Tests on concrete cylindrical specimens made with a specific SCC mixture have been performed first, showing that shrinkage and creep deformations are greater than predicted by European Model Code 1990 provisions. Longterm tests on reinforced SCC beams have also been performed according to the four-point bending scheme. The maximum stress on concrete in compression was approximately 35% of strength at the time of loading (37 days). The time evolution of midspan deflection as well as the strains at the compressive and tensile sides have been recorded. The beam deflection has been compared with the predictions by existing analytical models. The creep strength interaction has been also investigated by performing failure tests on control beams before and after long-term tests, and comparing them with tests on beams subjected to long-term loading. A small flexural strength increase with age at testing has been observed from the comparison of failure tests. It is related on a small compressive strength increase due to concrete aging, whereas the damage due to long-term loading previously applied was not significant.

Neuro-fuzzy based prediction of the durability of self-consolidating concrete to various sodium sulfate exposure regimes

Among artificial intelligence-based computational techniques, adaptive neuro-fuzzy inference systems (ANFIS) are particularly suitable for modelling complex systems with known input-output data sets. Such systems can be efficient in modelling non-linear, complex and ambiguous behaviour of cement-based materials undergoing single, dual or multiple damage factors of different forms (chemical, physical and structural). Due to the well-known complexity of sulfate attack on cement-based materials, the current work investigates the use of ANFIS to model the behaviour of a wide range of self-consolidating concrete (SCC) mixture designs under various high-concentration sodium sulfate exposure regimes including full immersion, wetting-drying, partial immersion, freezing-thawing, and cyclic cold-hot conditions with or without sustained flexural loading. Three ANFIS models have been developed to predict the expansion, reduction in elastic dynamic modulus, and starting time of failure of the tested SCC specimens under the various high-concentration sodium sulfate exposure regimes. A fuzzy inference system was also developed to predict the level of aggression of environmental conditions associated with very severe sodium sulfate attack based on temperature, relative humidity and degree of wetting-drying. The results show that predictions of the ANFIS and fuzzy inference systems were rational and accurate, with errors not exceeding 5%. Sensitivity analyses showed that the trends of results given by the models had good agreement with actual experimental results and with thermal, mineralogical and micro-analytical studies.