Conventional Vibrated Concrete Research Articles

New empirical test method to assess Reynolds dilatancy of concrete under free-surface flow

In this study, a new test method was proposed to evaluate the shear-induced volumetric changes, namely Reynolds dilatancy (RD), of sixteen conventional vibrated concrete (CVC) mixtures under free-surface flow. The RD measurements were carried out using a rheometer set-up and different vane-blade types rotating at different speeds. According to the experimental results, the RD values were found in good agreement with the workability of the investigated mixtures. Moreover, the RD values were well correlated with the coupled effect of the relative solid packing fraction of coarse aggregate (φ/φmax) and viscoplastic properties of the investigated CVC mixtures. Furthermore, a strong correlation was established between the rheological properties of the lubrication layer, RD values, and the φ/φmax of coarse aggregate.

Bond Strength of Reinforcing Steel Bars in Self-Consolidating Concrete

This paper presents an experimental investigation of the bond strength of reinforcing steel bars in tension in self-consolidating concrete (SCC). The effects of the reinforcing bar’s location, orientation, size, and coating on the bond strength with SCC were studied and compared to those with conventionally vibrated concrete (CVC). Several SCC mixtures were developed to cover a wide range of applications/components and material types. The fresh properties of the SCC mixtures were determined to evaluate their filling ability, passing ability and stability. Two hundred and thirty-four pull-out tests of rebars embedded in cubes, wall panels and slabs were conducted. Almost half of the tests were conducted to evaluate the bond with SCC and the other half with CVC. Load–slippage relationships were measured for each test. Pull-out test results were analyzed, and the bond strength was reported in two values: critical strength, which corresponds to slippage of 0.01 in. *0.25 mm); and ultimate strength, which corresponds to the maximum load. The critical strength of SCC and CVC were compared against the ACI 318-19 provisions and comparisons between the ultimate strength of SCC and CVC were conducted. The comparisons indicated that SCC has lower bond strength with vertical rebars than CVC, and a 1.3 development length modification factor is recommended. A similar conclusion applies to epoxy-coated and large diameter rebars. Also, SCC with high slump flow has shown a less top-bar effect than that of CVC.

The effect of finely ground dune sand on the properties of self-compacting concrete

Self-compacting concrete (SCC) is a unique concrete that has been developed over the past thirty years. They have the distinct characteristic of being very fluid. SCC differs from conventional vibrated concrete (CVC) in that it is incredibly fluid and doesn't require vibration. In order to reduce the amount of cement required by the increase in paste volume required to allow the concrete to flow, self compacting concretes require a large volume of mineral input. The main goal of this research was to ascertain how replacing cement with crushed dune sand (Sd) affected the SCC's physical and mechanical characteristics. The outcomes show that using crushed dune sand in self-compacting concrete produces interesting outcomes in terms of water absorption and compressive strength.

Use of concrete shear box for measuring the Bingham parameters of SCC

Flow characterization and controlling of fresh property of Self-compacting concrete (SCC) is most critical than conventional vibrated concrete (CVC) since slight variation in ingredients can have adverse effect on fresh properties, strength and durability of hardened concrete. Therefore rheological studies are important to overcome the insufficiencies of empirical tests.In the present work, the Bingham parameters of SCC were assessed by using the new instrument concrete shear box. The mixes were designed based on absolute volume concept starting with a volumes of paste (Vp). Three different Vp 0.37, 0.39 and 0.41 with water contents of 175 and 195 lt/m3 and cement contents of 300 and 450 kg/m3 along with GGBS as filler was used. Normal stresses of 0.10, 0.20 and 0.30 MPa along with three different displacement rates of 1, 5 and 15 mm/min were used under static load condition. The result indicate the usefulness of concrete shear box, as an additional instrument for measuring the Bingham parameters of SCC viz., yield stress and plastic viscosity and invalidates the use of Bingham model with higher flowability of 800 mm and beyond.

Analytical and Experimental study on load-deflection characteristics of Ternary blend SCC beams

Development of newer concrete is the need of the hour to meet out today’s demand due to fast growing construction activities. Taller constructions with lesser space involve closer reinforcements lead to suffer the reach of concrete uniformly. Hence concrete with higher degree of flowability without compromising strength comes to the mind of constructor. Such concrete called self-consolidating or compacting concrete and is capable of compacting on its own with no external effort. This paper deals with load deflection performance of such concrete using mineral and chemical admixtures, so that good amount of cement will be minimized without compromising strength and workability. Detailed experimental investigations were done with industrial wastes as replacers to conventional binder (cement) in ternary form. Experimental results of ternary SCC was compared with the results of conventionally vibrated concrete (CVC). Finite element model was developed using ANSYS and was validated with experimental results. It was inferred that ternary SCC beams exhibited more ductile nature compared to CVC beams.

Evaluating corrosion deterioration in self-compacted reinforced concrete beams and prisms using different tests

There is a limited reported research on the corrosion deterioration of self-compacted concrete (SCC) compared to conventional vibrated concrete (CVC). Therefore, this work represents a novel and innovative research to evaluate the corrosion deterioration of reinforcing steel in SCC compared to CVC using different tests. Sixteen reinforced concrete (RC) beams (100 × 150 × 1000 mm) and 16 RC prisms (100 × 100 × 400 mm) were casted using two w/c ratios (0.35 and 0.45) and two concrete types (SCC and CVC). After 28 days of moist curing, the beams and prisms were exposed to accelerated corrosion process using direct current supply. Different tests were performed to detect the corrosion deterioration in the RC specimens including crack pattern and width, ultrasonic pulse velocity (UPV), half-cell potential (HCP), and structural performance (flexural test for beams and pullout test for prisms).The innovative study showed that the SCC specimens (beams and prisms) exhibited higher performance in controlling the corrosion in comparison with CVC beams and prisms. The non-destructive tests (UPV and HCP) showed significant difference between the corroded SCC and CVC specimens. The damage index of the UPV of the corroded CVC beams showed higher values than that of the corroded SCC beams. The HCP values of the corroded CVC beams showed lower negativity than those of the corroded SCC beams. Flexural tests of corroded SCC beams showed higher performance than those of corroded CVC beams. Pullout behavior of corroded SCC prisms showed higher performance compared to corroded CVC prisms. As expected, the CVC and SCC specimens at w/c of 0.35 showed improved corrosion performance compared to the CVC and SCC specimens at w/c of 0.45.

The Interface Behavior of Rock, Conventional Vibrated and Roller Compacted Concrete

The interface behavior of rock and concrete and between layers of concrete highly affects the performance of concrete dam structures. In this investigation, a modified direct shear test was implemented in the laboratory to evaluate the interface behavior between (1) rock and conventional vibrated concrete (CVC), (2) rock and roller compacted concrete (RCC), (3) CVC and RCC and (4) two layers of RCC. Series of in situ shear tests were also performed between rock and concrete. The friction angle and cohesion for all tested interface were determined and analyzed. The effect of uniaxial compressive strength (UCS) of concrete on the interface behavior was determined. Additionally, the effect of surface roughness on the interface behavior was studied by determining the joint roughness coefficient values. The rock-CVC interface had a higher shear strength than the rock-RCC interface and the RCC–RCC interface had a significantly higher cohesion than the CVC–RCC interface. The peak friction angle equation for the rock joints was verified for rock-concrete interfaces. The high shear stress at the interface increases the dissipated energy. Based on the investigation, the rock-CVC interface with the highest concrete UCS had the highest cohesion, shear strength, and dissipated energy among the laboratory rock-concrete interfaces.

Use of industrial waste as partial fine aggregate replacement in SCC

In the current scenario, SCC is used in the variety of massconcreting applications. But SCC involves usage of more quantities of binder and fine aggregate content compared to conventionally vibrated concrete (CVC). The availability of basic constituent materials required for preparing the concrete in the entire world is facing a majorcrisis. For example, the construction industry has faced the non-availability of river sand since it is the principal ingredient that contributes the homogeneity in concrete. The experimental investigation was planned with the total of ten SCC mixes using industrial wastes namely copper slag (CS) and steel slag (SS) from 0% to 50% (with an increment of 10%) as fine aggregate replacement along with one control SCC (SCC0). The water-powder (w/p) ratio of 0.38, the dosage of Super plasticizer (SP) as 1.5% by the weight of cement and viscosity modifying agent VMA as 0.15% by the weight of cement were arrived based on the laboratory test trials. The fresh property tests were conducted in greener SCC according to EFNARC guidelines. The mechanical properties(compressive strength and split-tensile) were determined after 28 days of curing. Keywords: Compressive strength; copper slag; self-compacting concrete; splitting tensile strength; steel slag.

How much is bulk concrete sheared during pumping?

Pumping is an efficient procedure to place concrete inside formworks. Practical guidelines have been developed to facilitate this process for over half a century, and in the last decades, a more scientific approach has been applied to study the flow behavior of concrete in pipes. With the development of self-consolidating concrete (SCC), some substantial differences in the flow patterns of SCC and pumpable conventional vibrated concrete (CVC) have been discovered. Generally, SCC is said to be sheared during pumping, while for CVC, the shearing is only concentrated in the lubrication layer and the bulk concrete flows as a plug.This paper discusses the factors affecting the shear rate in the bulk concrete, and the additional flow rate caused by shearing the bulk concrete. The discussion is based on theoretical analyses and experiments described in literature. Increasing the ratio of the viscous constant of the lubrication layer to the viscosity of the bulk concrete increases the shearing in the bulk concrete. This appears to be the case for mixtures with lower w/cm. Increasing the bulk concrete yield stress to viscosity ratio, by using less flowable concrete mixtures, increases the plug flow and thus decreases the shear rate in the bulk concrete. However, the simple distinction between SCC is sheared and CVC remains unsheared is not valid. For certain sets of parameters, CVC can be sheared as well.

Study on Strength Characteristics of Binary Blend Self Compacting Concrete Using Mineral Admixtures

Self-compacting concrete (SCC) is the flowable concrete which tends to fill the formwork under its weight without external compaction. In the present research, 9 different SCC mixes in binary blend along with control SCC and conventional vibrated concrete (CVC) mixes were developed. In binary combination, cement was partially replaced by SF from 7 to 21%, MK from 10 to 30% and GGBS from 20 to 60%. For the above 9 combinations of SCC mixes, the basic rheological properties test namely slump flow and T500 were carried out in the fresh state of SCC. The flowability was achieved using Superplasticizer and viscosity modifying admixture (VMA), added by the percentage of the weight of cement. In hardened state, the compressive strength of the cube specimens and the split tensile strength of the cylinder specimens were carried out.

Restrained shrinkage cracking of self-consolidating concrete roads

Abstract The present study is dedicated to investigate the liability of continuously reinforced concrete pavement (CRCP) cast with self-consolidating concrete (SCC) to restrained shrinkage cracking and the values of restraint stresses in these pavements. SCC, which is becoming increasingly popular due to its several superiorities over conventionally vibrated concrete (CVC), has higher amounts and rates of shrinkage compared to CVC. The higher risk of restrained shrinkage cracking of SCC is a great cause of concern in pavement construction as the penetration of water, chemicals, and salts increases the risk of corrosion of reinforcement. In the present study, an analytical restraint stress expression was developed for typical CRC pavements by modifying the restraint stress equation developed previously for RC beams. Using this equation, the restraint stresses induced to the longitudinal reinforcement by the rigid pavement, cast with CVC or SCC, were calculated for eight different example sections. These restraint stress values were found to reach up to 50% of the limit stresses of bars, allowed by the design guidelines, when the pavement is cast with SCC. The amounts of longitudinal reinforcement used in typical CRCP roads were found to be more critical when the pavement is cast with SCC.

Comparative study on flexural behaviour of RCC beam and SCC ternary beams with mineral admixtures

Self compacting concrete (SCC) has an ideal fluid character at the fresh state and becomes solid once it sets/hardens completely when poured on the desired shape of the mould. The increase of workability and the control of segregation were taken care by super plasticizer (SP) and viscosity modifying agent (VMA) dosages. In this paper an attempt was made to study the flexural behaviour of ternary SCC beams. Cement was replaced with two different combinations viz metakaolin (mk)+ground granulated blast furnace slag (ggbs) and silica fume+ggbs. The experimental results of these ternary beams were compared with Conventional Vibrated Concrete (CVC) & SCC control concrete (SCC 0). Fresh properties of SCC like slump flow, spread were studied in accordance with EFNARC guidelines. Flexural strength of concrete was tested at the age of 28days. Load-deflection characteristics were studied at mid span of the beam (L/2). From the results it was observed that SCC ternary blended beams have higher flexural strength and better ductile performance compared to CVC and SCC0 beams.

Experimental study of the mechanical behavior of self-compacting concrete based on fracture mechanics

ABSTRACT Considering the physical nonlinearity of concrete and the fundamentals of fracture mechanics for quasi-brittle materials, the objective of this study was to determine the fracture energy and the length of the fracture process zone (FPZ) as well as the modulus of elasticity, the tensile strength and the compressive strength of self-compacting concrete (SCC) to characterize its mechanical behavior. A series of tests, including a three-point bending test of SCC and conventional vibrated concrete (CVC) specimens, with a notch at mid-span, and tensile and compressive tests were performed. The mechanical parameters obtained from the CVC specimens were considered as a comparative reference. The effect of the following variables was evaluated and considered at two levels: compressive strength (30 and 50 MPa), granular composition (fine and coarse particle size) and maximum diameter of the aggregate (12 and 20 mm). The effect of these variables on the mechanical behaviors of the SCC specimens was evaluated based on the test results of specimens of four types of concrete, which were obtained from the combination of the variables. The bending tests were performed according to the RILEM TC 89-FMT recommendations, which are based on the size-effect method.

Effects of Aggregate Properties on Rheology of Self-Consolidating Concrete

Abstract Compared with conventionally vibrated concrete (CVC), the rheological properties of self-consolidating concrete (SCC) should be closely controlled in order to satisfy fresh property requirements. Rheology of concrete is normally described by Bingham model. To investigate the effects of various aggregate properties on rheology of SCC, 25 mixtures were studied. It was found that higher aggregate volume, higher fine aggregate to coarse aggregate ratio, smaller aggregate size, and lower aggregate packing density may increase yield stress of SCC mixture. Aggregate size has an insignificant effect on plastic viscosity. Mixtures with slump flow less than 580 mm exhibited anti-thixotropy manner, whereas mixtures with slump flow 630 mm or higher showed thixotropy manner. No clear correlation was observed between plastic viscosity and T50 and Tf in the slump-flow test.

How do concrete rheology, tribology, flow rate and pipe radius influence pumping pressure?

Finding the critical factors that influence the pressure during pumping of concrete has been investigated for years. From fluid mechanics, the relationship between pressure and flow rate, radius or viscosity is known. In the practical guidelines for pumping of conventional vibrated concrete (CVC) the viscosity term is replaced by the concrete yield stress. However, recently, the influence of viscosity on pumping pressure has been reevaluated for self-consolidating concrete (SCC).In this paper, the influence of concrete rheology, tribology, flow rate and pipe radius on pumping pressure are discussed, based on full-scale pumping tests. The concrete mixtures varied from pumpable CVC to segregating SCC. The influence of flow rate and viscosity on pumping of concrete has been confirmed. It is also shown that with a 20% decrease in pipe radius (from 125 to 100 mm), the pumping pressure can be roughly doubled. An increase in yield stress also increases the pumping pressure, but its influence is only visible when the viscosity is approximately constant. The total flow resistance in the tribometer also appears to correlate well with the pumping pressure, proving that the developed tribometer mimics quite well the flow of concrete in a pipe.

Seepage and stress analysis of anti-seepage structures constructed with different concrete materials in an RCC gravity dam

This study used the finite element method (FEM) to analyze the stress field and seepage field of a roller-compacted concrete (RCC) dam, with an upstream impervious layer constructed with different types of concrete materials, including three-graded RCC, two-graded RCC, conventional vibrated concrete (CVC), and grout-enriched vibrated RCC (GEVR), corresponding to the design schemes S1 through S4. It also evaluated the anti-seepage performance of the imperious layer in the four design schemes under the normal water level and flood-check level. Stress field analysis of a retaining section and discharge section shows that the maximum tensile stress occurs near the dam heel, the maximum compressive stress occurs near the dam toe, and the stress distributions in the four schemes can satisfy the stress control criteria. Seepage field analysis shows that the uplift pressure heads in schemes S3 and S4 descend rapidly in the anti-seepage region, and that the calculated results of daily seepage flow under the steady seepage condition in these two schemes are about 30%–50% lower than those in the other two schemes, demonstrating that CVC and GEVR show better anti-seepage performance. The results provide essential parameters such as the uplift pressure head and seepage flow for physical model tests and anti-seepage structure selection in RCC dams.

A reaction-diffusion modeling of carbonation process in self-compacting concrete

In this paper, a reaction-diffusion model of carbonation process in self-compacting concrete (SCC) was realized with a consideration of multi-field couplings. Various effects from environmental conditions, e.g. ambient temperature, relative humidity, carbonation reaction, were incorporated into a numerical simulation proposed by ANSYS. In addition, the carbonation process of SCC was experimentally investigated and compared with a conventionally vibrated concrete (CVC). It is found that SCC has a higher carbonation resistance than CVC with a comparable compressive strength. The numerical solution analysis agrees well with the test results, indicating that the proposed model is appropriate to calculate and predict the carbonation process in SCC. The parameters sensitivity analysis also shows that the carbon dioxide diffusion coefficient and moisture field are essentially crucial to the carbonation process in SCC.

Durability Indicators Comparison for SCC and CC in Tropical Coastal Environments.

Self-compacting concrete (SCC) demands more studies of durability at higher temperatures when subjected to more aggressive environments in comparison to the conventional vibrated concrete (CC). This work aims at presenting results of durability indicators of SCC and CC, having the same water/binder relations and constituents. The applied methodologies were electrical resistivity, diffusion of chloride ions and accelerated carbonation experiments, among others, such as microstructure study, scanning electron microscope and microtomography experiments. The tests were performed in a research laboratory and at a construction site of the Pernambuco Arena. The obtained results shows that the SCC presents an average electrical resistivity 11.4% higher than CC; the average chloride ions diffusion was 63.3% of the CC; the average accelerated carbonation penetration was 45.8% of the CC; and the average open porosity was 55.6% of the CC. As the results demonstrated, the SCC can be more durable than CC, which contributes to elucidate the aspects related to its durability and consequent prolonged life cycle.

Prediction of pumping pressure by means of new tribometer for highly-workable concrete

Predicting pressure during pumping has received special attention in recent years. For conventional vibrated concrete (CVC), Kaplan et al. developed a tribometer to characterize the properties of the lubrication layer that is formed when concrete flows in a pipeline, to predict pressure. As this approach is limited to CVC, a new tribometer and data treatment procedure were recently developed by the authors, extending this approach for highly-workable concrete.This paper describes full-scale pumping tests undertaken to validate the tribological properties of the lubricating layer, determined using the novel tribometer. The program involved pumping 25 concretes, including 18 self-consolidating mixtures in a 30m long loop. The paper describes the pump, circuit, pressure and flow rate measurements, and the employed rheometer and tribometer, which are needed to predict pumping pressure. The results show that the model developed by Kaplan et al. accurately predicts pressure losses, confirming that the developed tribometer delivers accurate results for highly-workable concrete. Furthermore, it is shown that the assumption employed for CVC where the concrete flows as a plug surrounded by the lubrication layer is not always true, as the occurrence of plug flow depends on pumping characteristics, pipe diameter and concrete rheological and tribological properties.

Optimization of concrete I-beams using a new hybrid glowworm swarm algorithm

In this paper a new hybrid glowworm swarm algorithm (SAGSO) for solving structural optimization problems is presented. The structure proposed to be optimized here is a simply-supported concrete I-beam defined by 20 variables. Eight different concrete mixtures are studied, varying the compressive strength grade and compacting system. The solutions are evaluated following the Spanish Code for structural concrete. The algorithm is applied to two objective functions, namely the embedded CO2 emissions and the economic cost of the structure. The ability of glowworm swarm optimization (GSO) to search in the entire solution space is combined with the local search by Simulated Annealing (SA) to obtain better results than using the GSO and SA independently. Finally, the hybrid algorithm can solve structural optimization problems applied to discrete variables. The study showed that large sections with a highly exposed surface area and the use of conventional vibrated concrete (CVC) with the lower strength grade minimize the CO2 emissions.