Properties Of Self-compacting Concrete Mixes Research Articles

Forecasting the rheological state properties of self-compacting concrete mixes using the response surface methodology technique for sustainable structural concreting.

It is structurally pertinent to understudy the important roles the self-compacting concrete (SCC) yield stress and plastic viscosity play in maintaining the rheological state of the concrete to flow. It is also important to understand that different concrete mixes with varying proportions of fine to coarse aggregate ratio and their nominal sizes produce different and corresponding flow- and fill-abilities, which are functions of the yield stress/plastic viscosity state conditions of the studied concrete. These factors have necessitated the development of regression models, which propose optimal rheological state behavior of SCC to ensure a more sustainable concreting. In this research paper on forecasting the rheological state properties of self-compacting concrete (SCC) mixes by using the response surface methodology (RSM) technique, the influence of nominal sizes of the coarse aggregate has been studied in the concrete mixes, which produced experimental mix entries. A total of eighty-four (84) concrete mixes were collected, sorted and split into training and validation sets to model the plastic viscosity and the yield stress of the SCC. In the field applications, the influence of the sampling sizes on the rheological properties of the concrete cannot be overstretched due to the importance of flow consistency in SCC in order to achieve effective workability. The RSM is a symbolic regression analysis which has proven to exercise the capacity to propose highly performable engineering relationships. At the end of the model exercise, it was found that the RSM proposed a closed-form parametric relationship between the outputs (plastic viscosity and yield stress) and the studied independent variables (the concrete components). This expression can be applied in the design and production of SCC with performance accuracies of above 95% and 90%, respectively. Also, the RSM produced graphical prediction of the plastic viscosity and yield stress at the optimized state conditions with respect to the measured variables, which could be useful in monitoring the performance of the concrete in practice and its overtime assessment. Generally, the production of SCC for field applications are justified by the components in this study and experimental entries beyond which the parametric relations and their accuracies are to be reverified.

Effect of using dimensional stone waste sourced from Lorestan Province on the performance of high-strength self-compacting concrete

Producing enormous quantities and continuous stockpiling of granite industrial by-product enforced researchers to utilize this waste in a sustainable state in concrete to diminish its adverse impacts on the ecosystem. This study aims to experimentally investigate the possibilities of reusing granite waste sourced from Lorestan Province in fiber-reinforced self-compacting cementitious composite using hooked-end steel fibers. The L-box and U-box tests were performed to assess the fresh properties of mixes, whereas compressive strength, flexural strength, ductility, flexural toughness, and tensile strength tests were conducted for measuring the hardened properties of self-compacting concrete mixes. Results of the fresh properties tests for all of the steel fiber reinforced-recycled aggregate mixtures were found within the satisfactory limit of standard. In other words, the incorporation of granite waste in self-compacting concrete augmented the hardened properties. It should be noted that the effects of simultaneous use of granite waste and steel fiber in improving the tensile strength, flexural performance, ductility, and bending toughness of the specimens are higher than the compressive strength. In specimens without steel fiber, brittle failure occurred immediately after the formation of the first crack. With the increasing percentage of steel fibers in the samples, the ductility increased, and the ductile failure occurred in samples.

Effect of bottom-up placing on bond properties of high-performance self-compacting concrete

The characteristic rheological properties of self-compacting concrete mixes allow for their placing in variants other than the traditional one – from the top of a formwork. This paper presents the results of a study on the effect of different casting directions – from the top and bottom of a form – of a self-compacting mix on the bond phenomenon between reinforcement steel and high-performance selfcompacting concretes (HPSCC). Three HPSCC mixes having different contents of a mineral additive in the form of silica fume (replacing 0, 5 and 10% of the cement's mass) have been used to produce test elements. The elements had dimensions of 160 × 480 × 1600 mm. Ribbed steel reinforcing bars with diameters of 16 mm were used and fixed in formworks perpendicularly to the concrete placing direction. Bond tests were carried out following the pull-out method. This article analyses the impact of the concrete casting direction on: the compressive strength of the HPSCCs, the bond stiffness, the bond strength, the effect of the distance from the casting point and the top-bar effect. The tests on the elements cast in the bottom-up direction revealed an improvement of both the compressive strength and the rebar-to-concrete bond properties in the upper parts of the elements as compared to the traditional concreting. Placing from the bottom of the form offered uniformity of the bond conditions along the heights of the specimens studied in this experiment. Given the wider and wider implementation and a lack of any normative references for these concretes and alternative casting directions, the authors argue in favour of taking into account the concrete placing direction in the standard recommendations regarding the assessment criteria of the bond condition quality.

INFLUENCE OF VISCOSITY MODIFYING AGENT ON SOME RHEOLOGICAL PROPERTIES, SEGREGATION RESISTANCE AND COMPRESSIVE STRENGTH OF SELF-COMPACTING CONCRETE

Rheological properties of self-compacting concrete mixes containing a viscosity modifying agent (VMA) in their composition were studied. After preliminary studies self-compacting concrete mixes and, particularly, a fluid concrete mix prone to segregation of its ingredients were chosen. VMA was added in various amounts to that concrete mix to check how it performed in fresh and hardened concrete. Main studies focused on the influence of VMA on the following properties of concrete mixes: the slump flow, the flow time into the diameter of 500 mm and the resistance to segregation in the vertical direction. Moreover, the air content of concrete mixes and the 28-day compressive strength of concrete were measured. Test results showed that VMA significantly influenced the rheological properties of concrete mix, stabilised it and reduced the segregation. It was proved, that the concrete mix modified by VMA used in the optimal amount, featured the smallest scatter of concrete strength results. Besides, the Tukey's test showed that a reduction of the concrete compressive strength is possible to be statistically insignificant when compared to the reference level.

EFFECT OF SUPERPLASTICIZER DOSAGE ON WORKABILITY OF SELF COMPACT CONCRETE

Self-compacting concrete has an enhanced ability to flow. It is known to result in an increased segregation and bleeding potential. This paper discusses the results of an experimental investigation into the properties of self-compacting concrete mixes having varying dosage of high-performance superplasticizer (Glenium 51) (0.5%-3.0%) L per 100 kg of cement material. The properties investigated are workability on the fresh state of concrete by using one mix with five superplasticizer dosage (0.5%,1.0%,1.5%,2.5% and 3.0%) is used. The workability was assessed using three tests according to the specification of self compacted concrete (slump flow ,L- box differential height and V-funnel tests. The three dosage (1.0%,1.5% and 2.5%) comply with requirement for production of SCC while 0.5% and 3.0% don’t comply with specification requirement .Dosage of superplasticizer need to produce self compacted concrete range between (1.0%-2.5%) L/100 kg of cement according to the condition and material used in this paper

SCC mixes with poorly graded aggregate and high volume of limestone filler

Nonpozzolanic fillers are frequently used to optimise the particle packing and flow behaviour of cementitious paste in self-compacting concrete (SCC) mixes. This paper deals with the influence of finely ground limestone and crushed limestone dust on the properties of SCC mixes in the fresh and hardened state. Mixes were prepared using poorly graded crushed limestone aggregate. To compensate the lack of fine material in the crushed sand, a viscosity agent (VA) was added to the mixtures. The results obtained indicate that finer and better-graded limestone dust significantly increases the deformability of the paste. When a high volume of this filler was added to the SCC mix, the required self-compacting properties were achieved at a lower water/(cement+filler) ratio, and it also appeared that the addition of filler improves the 28-day compressive strength of concrete mixes due to the filler effect and improved fine-particle packing.