Assessing Molding Procedure of Compressive Strength Test Specimens for Self-Consolidating Concrete

Examination of cryogenic durability in self-consolidating concretes through mechanical and fracture mechanics approaches

Self-Consolidating Concrete (SCC) was used in the pre-tensioned box beams for the Stalnaker Run Bridge project in Elkin, WV. It was found that the SCC used in Stalnaker Run Bridge has a low freeze-thaw durability index. One of the SCC full-scale box beam was subjected to loading test at WVU structural laboratory until failure. Following the observed freeze-thaw behavior, this research study was proposed to quantify the SCC filling ability by saw-cutting the full-scale SCC test beam and to determine the cause of SCC beam's low freeze-thaw durability using the air-void analysis. Results from the coarse aggregate distribution analysis of the saw-cut cross sections and the core specimens of the SCC test beam show that the SCC beam exhibited significant segregation behavior. An air void analysis of the core specimens shows a high specific surface and spacing factor (SF); especially, the observed SF is about twice of the 0.2 mm suggested by ASTM C666. Additionally, the cored SCC beam specimens failed at 270 cycles, not meeting the ASTM C666 freeze-thaw requirement of 300 cycles. The permeability of the SCC was determined using the Rapid Chloride Penetration Test (RCPT) [ASTM C1202]. The results of the RCPT suggest that specimens from the test beam exhibited moderate chloride ion penetrability, which values higher than the allowable value of 1,500 Coulombs.;Laboratory SCC specimens were reproduced using the same mix design as was used for the SCC test beam. The laboratory cast SCC also exhibited a poor air void structure but with higher compressive strength. In order to better understand the durability effect of high temperature curing of SCC, half of the new casting specimens were cured at a higher temperature (as experienced by the SCC test beam) while half of the specimens were cured at room temperature. The compressive strength of high temperature cured SCC was higher for the first 3 days but lower at the 28 days compared to the room temperature cured specimens. The results indicated that high temperature curing had significant effect on concrete freeze-thaw durability and RCPT penetrability. The high temperature cured specimens failed at 270 freeze-thaw cycles while the room temperature specimens survived the 300 freeze-thaw cycles.

Recycled aggregate concrete is required owing to environmental conservation and actual consumption of resources. In the construction industry, for the manufacturing of concrete the demand for replacement of ordinary aggregates by recycled aggregates has increased worldwide due to the large quantity of structure and destruction waste. The objectives of this research is to evaluate the effects of strength of concrete by replacing the normal crush with different percentages such as 25%, 50%, 75% and 100% of recycled aggregates. To conduct this study, a total of 120 cylinders (60 for compression and 60 for splitting cylinder test) are casted with mixing ratio of 1:1.9:3.8 and water to cement ratio of 0.59 while curing is carried out for 7, 14, 21 and 28 days. Numerous laboratory tests are performed like workability test, compression tests and splitting tensile strength tests, to check and compare effects of the recycled aggregate concrete with reference mix M1 (0%RA). The results illustrate that the workability of concrete decreases when the quantity of recycled aggregates are increased due to more water absorbing capacity. Further, it is also perceived that the compressive strength of concrete is decreased by 3.8%, 5.7%, 12.9%, and 15.8% respectively at 28 days of curing by substituting coarse aggregates with various percentages such as 25%, 50%, 75% and 100% of recycled aggregates as compared to reference concrete mix M1 (0% RA). Similarly, splitting tensile strength is also decreased when the quantity of recycled aggregates in ordinary concrete is increased. Moreover, this reduction in workability and strength of concrete is due to more water absorbing capacity of recycled aggregates. Hence it is concluded from the research that up to 25% replacement of natural aggregate with recycled aggregates, the recycled aggregate concrete is usually preferable to reduce the cost of construction as well as improve the environmental pollution issues. It is also observed that the splitting tensile strength of a concrete batch should vary between 9 – 11% of its respective compressive strength test results.

This paper aimed to investigate the uniformity of in-place strength and compare the structural performance of beams cast with self-consolidating concrete (SCC) and reference concrete. Concrete mixtures with standard 28-day compressive cube strengths of 35 and 60 MPa were evaluated. These correspond to 2 classes of concrete: C35 and C60. The distribution of compressive strength from core samples along beams was also examined. The beams of reference mixtures were cast with external vibration and those made with SCC were cast without any compaction. In general, the in-place compressive strengths of SCC were closer to standard cube strength than those of ordinary concrete. The distribution of in-place properties along the beams was found to be uniform for both SCC and ordinary concrete, and the maximum strength difference was less than 7%. At service load, there were more and wider cracks with greater penetration with the reference mixture than with the SCC of Class C60. The mode of failure and load deflection response of the beams cast with SCC and ordinary concrete were similar.

In the design of new structures, EN 1992‐1‐1 normatively regulates the correlation between the compressive strength and tensile strength of concrete, in accordance with EN 206‐1. However, as there are many time‐ and load‐dependent impacts on existing structures, the relationship described by EN 1992‐1‐1 cannot be assumed without any further observations for existing structures. At the moment, there is no comprehensive investigation on the influences of, for example, subsequent hardening and carbonation on the concrete compressive or tensile strength. The tensile strength of concrete defined in EN 1992‐1‐1 is based on a water storage and a testing age of 28 days. Furthermore, the in‐situ tensile strength is affected by micro‐crack formation cause of internal stresses due to outflow of hydration heat, for example. Generally, there is a different influence of micro‐crack formation on the tensile strength of concrete than on the compressive strength of concrete. The actual value of the in‐situ tensile strength of concrete affects the shear force resistance and the load‐bearing capacity of anchors with concrete cone failure as decisive failure mode. Within the framework of a research project (SWD‐10.08.18.7‐13.01), financed by “Forschungsinitiative Zukunft Bau”, an initiative of the Federal Institute for Research on Building, Urban Affairs and Spatial Development (BBR) structural investigations on the correlation between the compressive and tensile strength of old concretes have been performed. Below, the results of the research project are presented.

The current article presents an experimental study on the use of two types of fly ash (low lime and high lime) as mineral admixtures in producing self-consolidating concrete (SCC) with the objective of assessing the effects of both types of fly ash on the fresh and hardened properties of SCCs. Within the scope of an experimental programme, SCCs were prepared by keeping the total mass of cementitious materials constant at 500 kg/m3, in which 30, 40, 50, 60 or 70% of cement, by mass, was replaced by high-lime and low-lime fly ash. The workability-related fresh properties of SCCs were observed through slump flow time and diameter, V-funnel flow time, L-box height ratio, GTM sieve stability test and the rheological parameters (relative yield stress and relative plastic viscosity). Setting times and temperature rise of SCCs were also determined as part of fresh properties. The hardened properties that were monitored for a year included the compressive strength, ultrasonic pulse velocity, drying shrinkage and chloride permeability. It was observed that the geometry and surface characteristics of fly ash affected the workability properties of SCC mixtures. Nonetheless, the compressive strength of SCC mixtures with 30–40% low-lime fly ash replacement was slightly greater than the control SCC mixture at the end of the year, as the amount of fly ash replacement increased losses in compressive strength. As a result of this experimental study, it could be concluded that SCCs incorporating a fly ash replacement of 70% could be produced with improved fresh and permeation properties and sufficient compressive strength.

Hot weather adversely affects the fresh, mechanical and durability properties of concrete. This study was conducted in an outdoor environment during the summer of 2014 at the construction material laboratory at Abu Dhabi University. The self-consolidating concrete (SCC) mixtures were continuously mixed for 2 h at temperatures ranging from 25 to 40°C, to simulate concrete in a transit truck during transportation to a construction site in hot weather. The paper displays the results of the fresh, mechanical and durability properties of SCC in hot weather. The SCC mixtures incorporated silica fume (SF) and fly ash (FA) in binary and ternary blends. A polycarboxylate-based high-range water-reducing admixture was used to maintain a consistent initial slump for all SCC mixes investigated. The flowability of SCC was evaluated using the slump flow test, visual stability index and T50. The concrete compressive strength was measured at 3, 7 and 28 d. The durability was evaluated using the rapid ion chloride penetration test. The results showed that both the fresh and mechanical properties of the SCC mixtures were highly affected by SF and FA dosage, temperature and prolonged mixing.

Classification of damage in self-consolidating rubberized concrete using acoustic emission intensity analysis

RETRACTED: The impact of GGBS and ferrous on the flow of electrical current and compressive strength of concrete

Statistical distributions of in situ microcore concrete strength

The concrete industry is considered environmentally unfriendly and unsustainable due to the significant consumption of natural materials. Currently, the industry predominantly uses Portland cement as its main ingredient, leading to an increase in Portland cement production. However, the use of fly ash can help make the concrete industry more sustainable in the future. Fly ash can be used as a partial replacement for Portland cement in concrete production. This study aims to determine the effect of fly ash variations on the compressive strength of reactive powder concrete. The research method used is experimental. The concrete mix design includes 30% quartz sand and fly ash variations of 0%, 5%, 10%, 15%, 20%, and 25%. The compressive strength test specimens are cylindrical with a diameter of 7.5 cm and a height of 15 cm. The resulting test specimens have a compressive strength of more than 41.4 MPa, thus qualifying as high-strength concrete. The compressive strength test results for fly ash variations of 0%, 5%, 10%, 15%, 20%, and 25% are 62.62 MPa, 66.27 MPa, 75.59 MPa, 68.78 MPa, 66.21 MPa, and 63.70 MPa, respectively.

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.

In this article, we considered the properties of self-consolidating concrete (SCC) into which both high-volume fly ash waste (FA) and high-volume recycled alumina waste (AW) were incorporated. FA was used as a cement substitution at 40% and 60%, and AW was used as a substitute for fine aggregate at 25%, 50%, 75%, and 100 %wt. The SCC blends were designed with the intention of creating a controlled flowing slump. In this study, the workability and mechanical properties of the blends were investigated by utilizing slump flow, J-ring flow behavior, blocking flow evaluation, V-funnel, compressive strength, and ultrasonic pulse velocity (UPV) estimations. The findings show that, compared with SCC without AW, the SCC blends that included AW required increased doses of superplasticizer and produced denser fresh concrete. With the increased cement content and altered FA content, the percentage of superplasticizer required and thickness of the fresh SCC decreased. When AW was incorporated at between 25% and 75%, its rheological and mechanical benefits became significant enough that including it in SCC became practical. Eventually, it is possible to manufacture SCC economically by using high volumes of FA and AW and even make it possible to develop green and environmentally friendly SCC.

The main purpose of this research was to compare the mechanical and durability characteristics of different self-consolidating concretes (SCC) produced with no fine materials nor viscosity-modifying agents with the respective properties of normally vibrated concretes (NVC) currently being in production. SCCs are manufactured with a high volume of sand containing a large proportion of fines. Eight concretes of the categories C20/25, C25/30, C30/37, and C45/55 were produced. The mechanical properties measured were the compressive strength, the splitting tensile strength, and the static modulus of elasticity. Durability of all concretes was assessed by measuring the water absorption, the carbonation coefficient, and the chloride diffusion coefficient. The results indicated that SCCs presented slightly increased compressive strength values when compared to the NVCs of the same class. Modulus of elasticity and splitting tensile strength measurements showed similar values in both SCC and the respective NVC. SCC performed better than NVC regarding their water absorption. Carbonation resistance and chloride diffusion resistance were similar among SCC and NVC.

This paper demonstrates the application of Random Forest (RF) algorithm for prediction of compressive strength of sustainable self-consolidating concrete (SCC) in which significant amount of cement was replaced with minerals such as fly ash, ground granulated blast furnace slag (GGBS), and silica fume. SCC improves the quality of the finished concrete product and is considered an environmentally friendly alternative to conventional concrete. RF proved capable of predicting compressive strength with high accuracy. The ability of RF algorithm to predict compressive strength established confidence on the experimental data itself which can be used for further studies on properties of self-consolidating concrete. The high level of accuracy in predicting essential engineering properties of concrete through RF algorithms offers important opportunities to enhance quality in ready mix production industry.