Powder-type Self-compacting Concrete Research Articles

Quartz Powder Valorisation in White Self-Compacting Concrete: Mortar Level Study

Quartz powder (QP) from mining exploration has increased, and valorisation solutions are sought. QP incorporation in structural concrete is an exciting strategy for the growth and sustainable development of the concrete industry, waste management and environmental protection. This work addresses the valorisation of QP from a Portuguese company on powder-type self-compacting concrete for architectural and structural purposes, combining the light colour of quartz with white cement. As such, QP was used as a partial cement replacement, acting as a filler on self-compacting white mortars (SCWM) and pastes (SCWP). Firstly, the QP was characterised by chemical, physical and morphological properties. Afterwards, SCWM with 10% of the white Portland cement with QP were produced and, with 10% cement replacement by limestone fillers, commercially available, for comparison purposes. The following engineering properties were evaluated, flowability and viscosity, electrical resistivity, porosity and mechanical strength. In equivalent pastes samples, the heat of hydration was accessed. Finally, an architectonic element prototype was produced using SCWM-QP, and colour and aesthetics were evaluated. All SCWM reached adequate deformability and viscosity for self-compaction. In the hardened state, compressive strength, electrical resistivity and water-permeable porosity presented similar results for mortars incorporating quartz powder and limestone fillers. The isothermal calorimetry in equivalent pastes revealed a slight desacceleration of hydration for SCWP incorporating QP. The major findings of this study confirm the feasibility of SCWM with QP, meeting the required performance while reducing resource depletion in the concrete industry and adding value to a by-product.

Self-compacting concrete produced with limestone waste

The aim of the research was to design powder type self-compacting concrete containing high amount of limestone quarry waste as aggregate and fines. The light colour aggregate mixed with white cement resulted in esthetical surfaces of exposed concrete for architectural purposes. Large amount waste originated from the limestone mining process requires deposition with further treatment. In our study we tried to replace also the limestone powder fines by the slurry produced during the cut of limestone blocks. Seven recipes were examined during the research: three mixtures of quartz aggregate with different particle size distributions were used as reference mixtures, three mixtures composed of crushed limestone aggregate and one with mixed quartz-limestone composition, respectively. In the recipe of mixed limestone-quartz aggregate dried quarry waste slurry was successfully applied instead of direct ground limestone powder. In the research different test methods were used to determine the fresh properties as well as the hardened properties of concretes.

Self-compacting concrete incorporating sugarcane bagasse ash

The aim of the current study is to assess the feasibility of incorporating sugarcane bagasse ash (SBA) from the sugar and ethanol industry as a filler material in the production of self-compacting concrete (SCC). For this purpose, paste composition was designed in the first stage of this study by conducting an experimental plan at the mortar level. During the second stage, SCC mixture properties were evaluated by considering the paste mixture proportions defined in the first stage. The study at the mortar level was conducted based on a statistical factorial design approach, which offers a valid basis for developing empirical models that allow determination of optimal settings of the design variables to satisfy all performance requirements. At the concrete level, the impact of three optimised paste mixtures on SCC properties was assessed. Fresh state, mechanical, and durability properties were evaluated. Mortar and concrete test results revealed that SBA can be used successfully in powder-type SCC as a filler material, and it exhibits good self-compacting ability and strength levels, which are adequate for many current civil engineering applications.

Shear strength of slender SCC beams - possible differences from VC beams

ABSTRACT In comparison with vibrated concrete (VC) of the same strength class, self-compacting concrete (SCC) typically has a lower coarse aggregate content and, eventually, a smaller maximum aggregate size. This may reduce the aggregate interlock between the fracture surfaces in SCC. Since the aggregate interlock plays an important role in the shear strength of slender beams, SCC beams may have a shear strength lower than that of similar VC beams. This article summarizes experimental studies on the shear strength of reinforced SCC slender beams without and with shear reinforcement. The shear strengths of SCC beams are compared with the ones of VC beams and also to the calculated ones according to different code procedures. It is shown that powder-type SCC beams tend to have lower shear strength than similar VC beams and that the difference depends upon the concretes composition and the characteristics of the beams.

Numerical optimization of self-compacting mortar mixture containing spent equilibrium catalyst from oil refinery

As the oil refining industries continue to grow, the production of waste catalysts generated in that process is expected to also increase. It would be of great value both economically and ecologically if these wastes could be reused as an addition in self-compacting concrete (SCC). This paper uses statistical factorial design approach, namely a central composite design, to conduct a proper experimental plan to design SCC mortar mixtures incorporating spent equilibrium catalyst (ECat), a waste generated by the oil-refinery industry. The mathematical empirical models derived (which were also experimentally validated) revealed the influence of mixture design parameters, and their coupled effects, on the mortars’ properties namely, deformability, viscosity, compressive strength, resistivity and ultrasonic pulse velocity. A numerical optimization technique was applied to the derived models to select the best mixture, which maximizes simultaneously durability and eco-efficiency and minimize cost, while maintaining self-compactability. The current study revealed that ECat can be successfully applied in SCC mortars, as a high volume cement replacement material (up toVEcat/Vp = 19.7%) due to its high pozzolanic activity. Nevertheless, for powder-type SCCs, cement/ECat blends must be combined with other finer additions to complete the powders distribution curve increasing the viscosity and stability of paste phase, in the fresh state.

Comparison of Shrinkage, Creep and Elastic Shortening of VMA and Powder Type Self-Compacting Concrete and Normal Vibrated Concrete

Self-compacting concrete (SCC) is flowing in nature and hence viscosity modified agent (VMA) or higher amount of binder is used for stability of mix. The mix proportion of SCC is also different from normal vibrated concrete (NC). This modifies the properties of concrete at fresh as well as at hardened state. Three mixes, one VMA type SCC, one powder type SCC and one NC, are considered with identical water to binder ratio. Properties at fresh state such as workability and segregation resistance and at hardened stage such as compressive strength, elastic modulus, shrinkage, creep and elastic shortening are determined and compared. Powder type SCC shows superior properties at fresh stage. Also compressive strength of powder type SCC is found better than that of VMA SCC and NC. Observations show more shrinkage, elastic shortening and creep for powder type SCC as compared with VMA SCC and NC.

Influence of self-compacting concrete fresh properties on bond to reinforcement

The paper presents a study on the influence of the fresh state behaviour of powder-type self-compacting concrete on the hardened properties when the formwork is filled by pumping from the bottom of the elements. More precisely the possible influence on concrete’s bond to reinforcement is investigated. For this purpose concretes classified in two different slump flow classes have been tested. The influence of the compressive strength was taken into account by using three compressive strength classes of concrete for each slump flow class. Moreover, three bar diameters have been considered. The results showed that the concrete fresh properties have a large influence on bond strength. The influence was observed for the end zone of the elements, and the bond behaviour is also sensitive to bar diameter.

Influence of the composition of powder-type SCC on conversion factors for compressive strength

Depending on practical considerations and standards, different types of test specimens are used for the determination of the uniaxial compressive strength of concrete. Appropriate conversion factors, also referred to as shape factors, are needed to convert the compressive strength as determined on one type of specimen to the equivalent compressive strength of another type of specimen. As such shape factors for vibrated concrete are influenced by the composition of the concrete, questions arise concerning the factors that affect the shape factors for powder-type self-compacting concrete (SCC). This paper describes the findings of an extensive research programme performed by three laboratories on the influencing parameters of the shape factors for SCC. Concrete composition parameters such as powder content, cement/powder ratio, water/cement ratio and the type of coarse aggregates, cement, filler and plasticiser appear to have little effect on the experimentally obtained shape factors. Any possible influence on compressive strength was overshadowed by experimental scatter.

Modification of existing shape factor models for self-compacting concrete strength by means of Bayesian updating techniques

In this paper, the existing formulas for the shape factors for uniaxial compressive strength of vibrated concrete, in which the influence of the shape, size and damage due to drilling has been included, are adapted for powder-type self-compacting concrete. An extensive test program was executed and Bayesian updating techniques were applied in order to calculate posterior distributions of the parameters involved in the conversion formulas for shape factors. Using this method, differences between the shape factor formulas of vibrated and self-compacting concrete could be analysed despite the large variability in the experimentally obtained test results. The methodology developed in this paper for the Bayesian updating of shape factor formulas can also be applied to other material properties of self-compacting concrete and even other materials, especially in cases where a limited number of samples are available or in cases where a considerable variability in the test data is observed.

Bond between powder type self-compacting concrete and steel reinforcement

The paper reports an investigation on the bond behavior between steel reinforcement and powder-type self-compacting concrete (SCC). A total of 135 pull-out cubes were cast by using four self-compacting mixes (SCC) and two vibrated concretes (VC). The main analyzed parameters were the concrete compressive strength, the reinforcement bar diameter, the embedded length of bars and cement/limestone ratio. The results showed that the ultimate bond strength can be greater in self-compacting concrete compared to vibrated concrete. At the same load level the bars in SCC tend to present a smaller slip than in VC. Considering the influence of bar diameter and embedded length, it seems that SCC and VC behave in a similar way.

Structural behaviour of powder-type self-compacting concrete: Bond performance and shear capacity

An experimental test program was carried out to investigate the bond and shear performance of powder-type self-compacting concrete (SCC). In order to examine the bond strength of reinforcement in concrete, pull-out tests (according to RILEM recommendation RC6 part 2) were performed. In total, 72 pull-out specimens were tested, cast with different concrete mixtures and rebar diameters (8, 12, 16, and 20mm). It was found that SCC shows normalized characteristic bond strength values as high as or higher than vibrated concrete (VC). In addition, as the bar diameter increases, larger bond strengths are measured, with the highest values for bars with diameter 12 or 16mm. When larger diameters up to 20mm are used, a decrease in bond performance is noticed. To study the shear behaviour, four-point bending tests were executed. Small SCC and VC beams were cast with different reinforcement ratios (1.0%, 1.5%, and 2.0%) and tested with different shear span-to-depth ratios (from 1.5 to 3.0), with a total of 102 beams. A slightly decreased shear capacity is observed for SCC. Also, higher ultimate shear stresses are recorded when higher reinforcement ratios or smaller shear span-to-depth ratios are applied.

Bond behaviour of reinforcing bars in self-compacting concrete: experimental determination by using beam tests

The force transfer between concrete and reinforcement depends on the bond characteristics between the two materials. Bond influences crack widths and the deflections of RC members and also determines anchorage and splice lengths. Self-compacting concrete (SCC) is characterized by a smaller amount of coarse aggregates when compared to conventional vibrated concrete. To investigate whether this change in mix design has a significant influence on the bond behaviour, a series of beam tests (according to RILEM recommendation RC6) was performed. A total of 36 specimens were cast using 3 different concrete types: one conventional vibrated concrete (CVC) and two powder-type SCC’s. The bond stress—slip behaviour of reinforcing bars with diameters ranging from 12 to 40 mm has been recorded. From these tests, it can be concluded that the bond strength of SCC is even higher than it is for CVC for small bar diameters, but the difference becomes smaller for larger bar diameters.

Integration approach of the Couette inverse problem of powder type self-compacting concrete in a wide-gap concentric cylinder rheometer: Part II. Influence of mineral additions and chemical admixtures on the shear thickening flow behaviour

The influence of mineral additions and chemical admixtures on the shear thickening flow behaviour of powder type self-compacting concrete (SCC) is studied by means of a wide-gap concentric cylinder rheometer. The Couette inverse problem is treated by means of the integration method in order to derive the flow curve τ(γ̇) from the torque measurements. According to the experimental results, the shear thickening effect is found to be strongly influenced by the addition of the chemical admixture (a polycarboxylate ether based superplasticizer), whereas mineral additions were found to modify the intensity of shear thickening. The limestone, quartzite and fly ash addition used in this research project, respectively increase, unalter and decrease the shear thickening intensity. The powder volume and the available amount of free water proved to have a major impact on the viscosity of the powder type SCC mixes. Increasing the powder volume or decreasing the amount of free water results in an increased viscosity of the SCC mix.

Time-dependent deformations of limestone powder type self-compacting concrete

Due to its different mix composition (e.g. use of superplasticizer, lower water/powder ratio (W/P) and higher paste volume) and its denser microstructure, different mechanisms and magnitudes concerning the time-dependent deformability, i.e. shrinkage and creep, hold for limestone powder type self-compacting concrete (SCC). For this reason, experimental investigations concerning the shrinkage and creep behaviour of 7 limestone powder type SCC mixtures and 1 reference, traditionally vibrated, concrete mixture (TC1) are performed. The water/cement ratio (W/C), cement/powder ratio (C/P), aggregate type and cement type are studied. The experimental data have been used to verify the accuracy of the CEB-FIP Model Code 1990 (MC-90) in terms of long-term deformations. Test results revealed generally higher shrinkage and creep deformations for the SCC mixtures compared with the TC1 mix. However, whereas the shrinkage deformations are underestimated by MC-90 the creep and overall behaviour of the limestone powder type SCC mixtures are rather well predicted by the same model. In order to properly predict the time-dependent behaviour of limestone powder type SCC in cases of concrete structures (highly) sensitive to shrinkage and creep, a modification of the MC-90 in terms of the total shrinkage strain prediction is proposed by the authors. For creep, test results revealed that the MC-90 creep coefficient prediction could remain unmodified for limestone powder type SCC application.

Deformability prediction model for self-compacting concrete

The aim of the current study is to propose a model for predicting deformability of powder-type self-compacting concrete (SCC) based on theoretical and empirical approaches. Deformability, one of the essential functions for SCC's filling ability, was defined and determined in this study to include deformation capacity, indicated by slump flow value, and velocity of deformation, measured by 500 mm slump flow time (T500). In the process of mix proportioning, both deformation properties should be considered to achieve good deformability. Prediction models for deformation capacity and velocity of deformation were developed based on the concepts of free water content, water retainability of solid particles and inter-particle forces in the concrete. It was found that slump flow and T500 varied mainly with free water content in mixtures and were also affected by various factors, such as ratio of paste volume to void content of compacted aggregate phase, surface area, shape and water retainability of powder materials and aggregates and efficiency and dosage of superplasticiser. Experimental results from the current authors and other researchers were used in the verification of the proposed models. It was evident that the proposed models could be used to predict the slump flow and T500 with satisfactory accuracy.

Integration approach of the Couette inverse problem of powder type self-compacting concrete in a wide-gap concentric cylinder rheometer

For powder type self-compacting concrete (SCC) mixes, commonly used in Belgium, a shear thickening (Herschel–Bulkley) flow behaviour of the fresh mixes is quite often observed. A longstanding problem in rheometry is the so-called “Couette inverse problem”, where one tries to derive the flow curve τ ( γ ˙ ) from the torque measurements T( N) in a (wide-gap) concentric cylinder (Couette) rheometer, with T the torque registered at the inner, stationary cylinder and N the rotational velocity of the outer, rotating, cylinder. In this paper, the Couette inverse problem is approached by means of the integration method in order to convert T( N) into τ ( γ ˙ ) for a wide-gap ( R o/ R i = 1.45) concentric cylinder rheometer. The approach consists in the decoupling of the flow resistance and the power-law flow behaviour after exceeding the flow resistance. The integration approach is validated by experimental verification with different powder type SCC mixtures. By means of illustration, the results of one limestone powder type SCC mixture with different superplasticizer contents are shown in this paper.