Properties Of Self-compacting Concrete Mixtures Research Articles

Development of High-Tech Self-Compacting Concrete Mixtures Based on Nano-Modifiers of Various Types.

Promising areas of concrete material science are maximum greening, reducing the carbon footprint, and, at the same time, solving the problems of increasing the cost of raw materials using industrial waste as modifiers for self-compacting concrete mixtures. This study aimed to review, investigate and test from the point of view of theory and practice the possibility of using various industrial types as a nano-modifier in self-compacting concrete with improved performance. The possibility of nano-modification of self-compacting concrete with a complex modifier based on industrial waste has been proved and substantiated theoretically and experimentally. The possibility of improving the technological properties of concrete mixtures using such nanomodifiers was confirmed. The recipe and technological parameters of the process were revealed and their influence on the characteristics of concrete mixes and concretes were expressed and determined. Experimental technological and mathematical dependencies between the characteristics of the technological process and raw materials and the characteristics of concrete mixtures and concretes were determined. The optimization of these parameters was carried out, a theoretical substantiation of the obtained results was proposed, and a quantitative picture was presented, expressed in the increment of the properties of self-compacting concrete mixtures using nano-modifiers from industrial waste concretes based on them. The mobility of the concrete mixture increased by 12%, and the fluidity of the mixture increased by 83%. In relation to the control composition, the concrete strength increased by 19%, and the water resistance of concrete increased by 22%. The ultimate strains decreased by 14%, and elastic modulus increased by 11%.

Vibration analysis of steel fiber reinforced self-compacting concrete beam on elastic foundation

In this study, the effect of steel fiber utilization, boundary conditions, different beam cross-section, and length parameter are investigated on the free vibration behavior of fiber reinforced self-compacting concrete beam on elastic foundation. In the analysis of the beam model recommended by Euler-Bernoulli, a method utilizing Stokes transformations and Fourier Sine series were used. For this purpose, in addition to the control beam containing no fiber, three SCC beam elements were prepared by utilization of steel fiber as 0.6% by volume. The time-dependent fresh properties and some mechanical properties of self-compacting concrete mixtures were investigated. In the modelled beam, four different beam specimens produced with 0.6% by volume of steel fiber reinforced and pure (containing no fiber) SCC were analyzed depending on different boundary conditions, different beam cross-sections, and lengths. For this aim, the effect of elasticity of the foundation, cross-sectional dimensions, beam length, boundary conditions, and steel fiber on natural frequency and frequency parameters were investigated. As a result, it was observed that there is a noticeable effect of fiber reinforcement on the dynamic behavior of the modelled beam.

COMPARISON OF FRESH AND HARDENED PROPERTIES OF SELF-COMPACTING CONCRETE MIXTURE FROM DIFFERENT ASPECT RATIO OF STEEL FIBER VIEW POINT

ABSTRACT Self-compacting concrete (SCC) is a type of concrete which is frequently preferred in different applications due to its advantages such as its fluidity and transition in tight openings between steel reinforcing bars. However, it is vital that SCC maintains its fresh state characteristics when its transportation phase is taken into consideration. Fiber reinforced in SCC affects the properties of fresh concrete negatively while it had a positive effect on its dynamic properties. In this study, the effect of steel fibers having different aspect ratios on the time dependent fresh properties and mechanical properties of self-compacting concrete mixtures was investigated. In addition to the control mixture without fiber, in the mixtures containing fiber, three different twin-hook steel fibers with aspect ratios of 54, 64 and 50 were used as 0.6% of total volume. In all of the SCC mixtures, the water/cement ratio, cement dosage and slump-flow value were kept constant. The time dependent rheological properties of the mixtures were investigated. The compressive, split-tensile and flexural strengths as well as fracture energy, the load deflection relation under flexural load and load-crack opening displacement, modulus of elasticity of SCC mixtures were also investigated. Besides, the water absorption capacity and depth of penetration of water under pressure of mixtures were measured. On the basis of the results, the fiber utilization and its aspect ratio had no significant effect on compressive strength and modulus of elasticity of the SCC mixtures. The split-tensile, flexural strengths and fracture energy of SCC mixtures increased by using fiber; the permeability properties of SCC mixture increased by fiber utilization.

Influence of mixing time and superplasticizer dosage on self-consolidating concrete properties

Self-compacting concrete (SCC) requires specific properties, such as fillability, flowability, and passability. It also needs to resist bleeding and segregation, which may be caused by increased water or superplasticizer (SP) content. In addition, long periods of mixing deteriorate the properties of fresh SCC and causes difficulty in filling structure sections. This study investigates the effect of different mixing periods (e.g., 15, 30, 60, and 90min from the addition of water to the mixture) and increased SP doses (e.g., 1.5%, 2%, 2.5%, and 3% of cement mass) on the properties of SCC mixtures. The properties of fresh concrete were assessed by seven tests, namely, slump flow, V-funnel, slump flow T50, V-funnel T5, L-box, bleeding, and segregation. Hardened concrete was assessed on the basis of compressive, indirect, and flexural strengths. Results showed that compared with the slump flow under 15min mixing time, the 30, 60, and 90min increase in mixing time reduced slump flow by 6%, 19%, and 27%, respectively. Findings also showed that results of SCC segregation and bleeding decreased when increased mixing time. The results also appeared that compressive strength of SCC slightly decreased compared with that under 15min mixing time. The increase in dosage of superplasticizer has mitigated the negative effect for long mixing periods on the properties of concrete.

Technological Properties of Self-Compacting Concrete Mixtures with Ground Quartz Sand

Quantitative parameters of influence of grain composition of ground quartz sand and its quantity on the workability and segregation of self-compacting fresh concrete were determined at the constant amount of mixing water and water-cement ratio. Ground quartz sand in the amount of 50-150 kg/m3 was added instead of fine and coarse aggregates with changing the amount of polycarboxylate superplasticizer. It is stated that the use of ground quartz sand of finer grinding provides higher values of workability at the same quantity of water and superplasticizer. Segregation of the fresh concrete occurs when using increased amount of ground quartz sand of coarser grinding and increased amount of superplasticizer. Experimental studies have shown the effectiveness of the use of ground quartz sand to obtain self-compacting fresh concrete of different classes of workability SF1 and SF2 as well as classes of segregation resistance SR1 and SR2. The results of the experiments allow to state that the use of ground quartz sand of coarser grinding leads to segregation of fresh concrete at its low workability, while the use of ground quartz sand of finer grinding allows to obtain fresh concrete with resistance to segregation.

Influence of accelerated carbonation curing on the properties of self-compacting concrete mixtures containing different mineral fillers

This paper presents a study on the effects of accelerated carbonation curing (ACC) on performance of self-compacting concrete (SCC) mixtures prepared using limestone powder (LSP) alone and blend of limestone powder and silica fume (SF) as mineral fillers. Specimens cast using both SCC mixtures were subjected to ACC that consisted of exposing specimens to CO2 for 10 hours under a constant pressure of 414 kPa. ACC-treated specimens were tested for evaluating effects of ACC on properties of SCC mixtures in terms of CO2 uptake, mechanical and durability properties, morphology, and mineralogy. Test results indicate that the ACC-treatment substantially enhanced the properties of both SCC mixtures. Strength of ACC-treated concrete specimens can be improved further by exposing them to air for a period of first 7 days of the ACC-treatment. ACC-treatment of LSP-SF-C was more effective than that for LSP-C. Properties of ACC-treated SCC mixtures were comparable with that of the same mixtures subjected to moist-curing for 7 days except drying shrinkage, which was higher for ACC-treated specimens than the moist-cured specimens. However, shrinkage of ACC-treated specimens after 7 days was within the permissible limit in case of LSP-C whereas 7-day shrinkage for LSP-SF-C exceeded the permissible limit of 500 µm.

Effects of the mechanical milling method on transport properties of self-compacting concrete containing perlite powder as a supplementary cementitious material

The purpose of this study is to measure the effects of increasing the specific surface area of perlite natural pozzolan in self-compacting concrete (SCC) by the mechanical milling method. The use of SCC in construction projects allows for a reduction of human resources and equipment, which significantly decreases the labor cost and time of construction. SCC often needs chemical additives to achieve workability requirements. However, the usage of a greater amount of chemical additives as well as cement materials in the mixing designs increases the cost of mixing. Incorporation of inexpensive natural pozzolans as an alternative to cementitious materials can improve the fresh properties and durability of concrete. Moreover, reducing the hydration heat and controlling the shrinkage of SCC mixtures, which mainly contain significant amounts of powdered materials, is another benefit of the natural pozzolans. However, the reactivity of natural pozzolans, specifically in the early ages, is always a concern when using these supplementary materials. In this study, several methods have been proposed to improve the reactivity of these materials. Increasing the specific surface area of pozzolanic materials by mechanical milling is one of the most economical and efficient methods implemented so far. This study measured the performance of various levels of perlite powder, a natural pozzolan, for fresh, mechanical and durability properties. In addition, the effects of increasing the specific surface area of perlite powder on properties of concrete were measured and evaluated. According to the results, an increase in the specific surface of perlite powder improved the compressive strength and durability index as a result of increased reactivity. This was accompanied by a substantial improvement in the properties of SCC mixtures in the workability and stability tests.

Fresh properties of self-compacting concrete with plastic waste as partial replacement of sand

This work aimed to investigate effecting of using plastic waste as partial replacement of fine aggregate, on the fresh characteristics of self-compacting concrete (SSC). For this purpose, different self-compacting concrete mixes were designed at constant water-to-binder ratio of 0.32 and 520 kg/m3 of binder content. Class F fly ash was used as partial replacement of cement (30% by weight of cement). The six designated plastic waste contents of 0, 2.5, 5, 7.5, 10, and 12.5% and three different sized Plastic wastes (fine plastic wastes, coarse plastic wastes, and mixed plastic waste) were considered as experimental parameters. The workability properties of self-compacting concrete mixtures were performed regarding to slump flow diameter, T50 slump flow time, V-funnel flow time, L-box height ratio, and L-box T20 and T40 flow times. The 28-day compressive strengths of self-compacting concretes were also measured. The experimental results of this work are showed that the plastic waste with the sizes and contents that used in this work can be used successfully as a fine aggregate in self-compacting concrete.

The possibility of enhancing some properties of self-compacting concrete by adding waste plastic fibers

An attempt was carried out to develop some properties of self-compacted concrete (SCC) by adding waste plastic fibers (WPF) resulting from cutting beverage bottles. Many tests were conducted to investigate the effect of adding WPF on the fresh properties, whereas other tests were applied on that kind of concrete to study the effect of this type of waste on hardened properties. For this reason, different self-compacting concrete mixtures were designed at constant water-to-binder ratio of 0.35 and 490kg/m3 of binder content. The class F fly ash was replaced with cement as 25% by weight. The eighth designated plastic fiber contents of 0%, 0.25%, 0.5%, 0.75%, 1%, 1.25%, 1.5%, 1.75% and 2% by volume. The workability properties of self-compacting concrete mixtures were performed to slump flow diameter, T50 slump flow simultaneously, V-funnel flow at the same time, and L-box height ratio. The 7, 14 and 28-day compressive strengths of self-compacting concretes were also measured. Moreover, the 7, 14 and 28-day flexural strengths of concretes were also measured. The test results showed that the plastic fibers have adverse effect on the fresh properties of self-compacting concrete and improvement by hardened properties.

Properties of self-compacting concrete mixtures containing metakaolin and blast furnace slag

Rheological, mechanical and durability properties of self-compacting concrete (SCC) mixes produced using blended binders containing metakaolin and blast furnace slag are studied. The rheological properties of SCC mix with metakaolin are characterized by significant yield stress and relatively low viscosity, while the mix with blast furnace slag shows zero yield stress and higher viscosity. The compressive strength of SCC with metakaolin grows very fast during the initial hardening period and remains significantly higher, as compared with the mix with blast furnace slag, up to 90 days. Durability properties of the mix containing metakaolin are excellent. Water absorption coefficient and water penetration depths are very low. The freeze resistance tests show zero mass loss after 56 cycles in deicing salt solution.