Durability of self-consolidating concrete to different exposure regimes of sodium sulfate attack

This study investigates the durability of a wide scope of self-consolidating concrete (SCC) mixture designs to sodium sulfate attack. The mixture design variables included the type of binder (single, binary, ternary and quaternary), air-entrainment, sand-to-aggregate ratio and hybrid fibre reinforcement. Since current standard test methods (e.g. ASTM C 1012) generally do not address various sulfate attack exposure scenarios that may exist under field conditions, three different sulfate attack exposure regimes (full immersion, wetting-drying and partial immersion) were investigated in the current study. In the wetting-drying and partial immersion exposure regimes, results of the physico-mechanical properties revealed performance risks associated with some SCC mixture designs. Such risks were not captured by the full immersion exposure. Thermal, mineralogical and microscopy studies elucidated the complexity of degradation mechanisms, which in some cases varied at different locations of the same specimen. Findings from this study emphasize the need for performance standard tests that can better simulate various realistic field exposure regimes in order to achieve a more reliable and comprehensive evaluation of the resistance of concrete to sulfate attack.     

Durability of self-consolidating concrete to combined effects of sulphate attack and frost action

The worldwide shift towards performance-based standards for concrete demands the advent of performance tests that combine more than one damage mechanism. Such tests can be more reliable in evaluating emerging concrete types such as self-consolidating concrete (SCC). Several applications of SCC involve its exposure to both freezing–thawing cycles and chemical attack, particularly to sulphate-rich media. This study aims at investigating the durability of SCC to sulphate attack coupled with frost action. Potential performance risks of SCC under this dual exposure were identified in terms of various mixture design parameters. Deterioration in physico-mechanical parameters was related to thermal, mineralogical and microscopy analyses, which demonstrated the complex mutual effects of sulphate attack and frost action on SCC specimens. It is shown that SCC mixtures that perform well under the classical ASTM C 1012 test can fail under coupled exposure to freezing–thawing cycles and sulphate attack.     

Image analysis applications on assessing static stability and flowability of self-consolidating concrete

A digital image processing (DIP) method associated with a MATLAB algorithm is used to evaluate cross sectional images of self-consolidating concrete (SCC). Two new parameters, such as inter-particle spacing of coarse aggregate and average mortar-to-coarse aggregate ratio, defined as average mortar thickness index (MTI), were proposed to quantitatively evaluate the static stability of SCC. Statistical models were developed to predict flowability of SCC mixtures. Test results revealed that the proposed DIP method and MATLAB algorithm can be successfully used to derive inter-particle spacing and MTI and quantitatively evaluate the static stability on hardened SCC samples. A probability density of 60% from histogram analysis appears to be a reasonable threshold for indicating a uniformly distributed SCC mixture. For a given mortar yield stress, a critical mortar viscosity of 1.30 Pa s tends to significantly affect the trend of slump flow changing with MTI. The investigated relationship between parameters measured from DIP method and existing theoretical frames is well correlated. The outcome of this study can be of practical value for providing an efficient and useful tool in designing mixture proportions of SCC.     

Rheological approach in proportioning and evaluating prestressed self-consolidating concrete

The successful development of self-consolidating concrete (SCC) requires a careful control of rheological properties of matrix. In this investigation, a parametric study was undertaken to evaluate the influence of binder type, w/cm (water-to-cementitious materials ratio), and coarse aggregate type and nominal size on rheology of prestressed SCC. The rheological measurement of the 33 SCC mixtures investigated in parametric study was performed using a modified Tattersall two-point workability rheometer. The yield stress and plastic viscosity values derived from the SCC mixtures were correlated to the various workability test results to identify combinations of rheological parameters necessary to secure adequate filling ability, filling capacity, and stability of SCC for successful casting of prestressed elements. Based on the results, it is recommended that SCC should have a plastic viscosity of 30–70 Pa s and 30–130 Pa s for concrete made with crushed aggregate and gravel, respectively, to ensure proper workability. Higher viscosity levels could lead to limitation in passing ability should be avoided. Better understanding of the rheological parameters that control the workability of SCC is important in developing mix design approaches and interpreting quality control test methods.     

Development of a tribometer to characterize lubrication layer properties of self-consolidating concrete

The last decade, significant advances have been made in investigating, understanding and predicting the flow characteristics during pumping of concrete. Kaplan developed theoretical equations based on the rheological and tribological properties of concrete to predict pumping pressures. Several tribometers were developed to characterize the flow properties of concrete along a smooth wall, but none of them allows the use of highly-workable concretes. The main reason is that for the calculation of the yield stress and viscous constant of the lubrication layer, the concrete is not allowed to be sheared.In this paper, a new design for the concrete tribometer is presented, along with a calculation procedure to eliminate the contribution of concrete shearing from the rotational velocity. In this way, the viscous constant can be calculated in the same way as for the previously developed tribometers. The analysis of the data reveals that the total flow resistance in the tribometer (I_trib) is well related to the plastic viscosity for SCC and to the yield stress for the other concretes, which is in line with practical results on the influence of rheology on pumping pressure. The viscous constant of the lubrication layer appears related to the plastic viscosity of SCC, but the paper shows that many mix design parameters influence this relationship.     

Using aggregate flowability testing to predict lightweight self-consolidating concrete plastic properties

This paper presents the results of an experimental study on the flow properties of lightweight self-consolidating concrete (LWSCC) which utilizes a new test relating aggregate flow to concrete flow. Three types of LWSCC were tested containing differing proportions of lightweight and normal weight, coarse and fine aggregates, as well as a normal weight self-consolidating concrete (NWSCC) as a control. The flow properties of the aggregate mixes used in the LWSCC and NWSCC specimens were tested using a V-funnel. The concrete flow properties were also tested for comparison, as were the compressive and tensile strengths of the various mixtures. A relationship between the aggregate frictional resistance and the traditional concrete flowability tests—i.e., slump flow, J-ring, and T₅₀₀—was demonstrated. Compressive strengths were greater in LWSCC mixes that contained smaller sized coarse and normal weight aggregates. Finally, a design procedure is introduced that utilizes the aggregate frictional resistance, paste flow properties, and aggregate void ratio to predict the plastic properties of the concrete.     

Effects of mix design parameters and rheological properties on dynamic stability of self-consolidating concrete

Stability is a crucial property for successful placement and performance of self-consolidating concrete (SCC). Dynamic stability refers to the segregation resistance of concrete during flow and is not thoroughly described in literature to date. In this research, a newly developed dynamic stability test, the Tilting-box test, was employed to evaluate the effect of different mix design parameters on the dynamic segregation of SCC. Paste volume, water-to-binder ratio (w/b), maximum size of aggregate (MSA), aggregate density, and aggregate grain-size distribution were shown to affect the dynamic stability of SCC, while the coarse aggregate shape did not have a significant influence. The slump flow and V-funnel flow time as well as the rheological parameters were found to be an efficient tool for controlling dynamic segregation. Higher yield stress or plastic viscosity reduced the risk of dynamic segregation. Recommended workability characteristics and rheological parameters of SCC to ensure adequate dynamic stability level were proposed.     

Mechanical behavior of hybrid steel-fiber self-consolidating concrete: Materials and structural aspects

This work presents the preliminary results of an experimental investigation on the mechanical behavior of self-consolidating concrete reinforced with hybrid steel fibers in the material and structural scale. Straight and hooked end steel fibers with different lengths and diameters were used as reinforcement in fiber volume fractions of 1.0 and 1.5%. In the fresh state the concrete was characterized using the slump flow, L-box and V-funnel tests. To determine the effect of the hybrid reinforcement on the plastic viscosity and shear yield stress a parallel plate rheometer was used. Following, the mechanical response was measured under tension and bending tests. In the flexural test, the movement of the neutral axis was experimentally determined by strain-gages attached to compression and tensile surfaces. Furthermore, the mechanical response of the material under bi-axial bending was addressed using the round panel test. During the test the crack opening was measured using three linear variable differential transformers (LVDT’s). The cracking mechanisms were discussed and compared to that obtained under four point bending and direct tension. The obtained results indicated that the fiber hybridization improved the behavior of the composites for low strain and displacement levels increasing the serviceability limit state of the same through the control of the crack width. For large displacement levels the use of the longer fibers led to a higher toughness but with an expressive crack opening. Due to its structural redundancy the round panel test allowed the formation of a multiple cracking pattern which was not observed in the four point beam tests. Finally, the obtained material’s properties were used in a nonlinear finite element model to simulate the round panel test. The simulation reasonably agreed with the experimental test data.     

Effect of cement type and limestone particle size on the durability of steam cured self-consolidating concrete

This paper describes a laboratory program to investigate the influence of cement and limestone filler (LF) particle size on the hardened properties and durability performance of steam cured self-consolidating concrete. In addition, the interplay between cement type and LF particle size was investigated. CSA (Canadian Standards Association) Type GU (General Use) and HE (High Early-strength) cements were used with 5% silica fume (SF) [1]. The water-to-cement ratio was 0.34. LF with two nominal particle sizes of 17 μm and 3 μm, which correspond to Blaine fineness of 475 and 1125 m²/kg, respectively, were used. In addition to fresh concrete properties, hardened properties including compressive strength, elastic modulus, ultrasonic pulse velocity and density were measured at 12 h and 16 h, and at 3, 7 and 28 days. Indicators of durability performance including rapid chloride permeability testing (RCPT), sulfate resistance, linear shrinkage, salt scaling resistance and freeze-thaw resistance were evaluated. The results showed that LF improved the 12 and 16-h strength with no influence on later age strength (i.e., 3–28 days). The linear shrinkage and RCPT decreased with the addition of LF. This reduction was linked to the production of calcium mono-carboaluminate. LF did not impact the sulfate resistance, salt scaling resistance or freeze-thaw resistance of concrete.     

Shear behaviour of steel fibre reinforced self-consolidating concrete beams based on the modified compression field theory

A series of steel fibre reinforced self-consolidating concrete (SFRSCC) beams have been tested to investigate the influence of steel fibres and the combined effect of fibres and stirrups on the deflection and cracking, ultimate loads and failure pattern. The experiment indicates that the shear strength increases clearly with the increasing of fibre content. The combination of steel fibres and stirrups demonstrates a positive composite effect on the ultimate load, ductility and failure pattern of concrete beam. This study also examines the feasibility of applying the modified compression field theory (MCFT) for the suitable assessment of shear resistance in fibre and steel rebar reinforced self-consolidating concrete beams. For fibre reinforced concrete member, a theoretical method is proposed based on the MCFT. The proposed ultimate shear capacity model was verified by the comparison with different test results.     

Durability of CFRP cables exposed to simulated concrete environments

One of the main causes of structural deficiency in concrete bridges is the deterioration of the constituent materials. Some transportation agencies have started exploring the use of carbon fiber reinforced polymers (CFRP) as a corrosion-resistant alternative to steel prestressing materials for longer lasting concrete bridge structures. To implement CFRP in prestressed concrete bridge structures with more confidence, an understanding of the challenges pertaining to durability under in-service environmental conditions is essential. This paper explores the effects of temperature with alkaline and alkaline/chloride solutions on material properties over time, in the context of reinforced and prestressed concrete structures for transportation applications. The durability testing yielded several key findings: (1) higher temperatures accelerate degradation, (2) moisture sorption was the primary process responsible for the observed degradation, with plasticization and microcracking as the controlling mechanisms leading to fiber–matrix interfacial debonding, and (3) a relaxation-based analytical model was implemented to predict residual properties after environmental exposure, showing promising agreement with experimental data.     

Gas permeability and capillary porosity of self-compacting concrete

Self-compacting concrete (SCC) can be placed without any external compaction avoiding some health risks as well as environmental problems. In order to obtain its key properties, a large amount of fine particles and a new generation of superplasticizers can be used. Earlier research by means of mercury intrusion porosimetry, already pointed out an important difference in pore structure between SCC and traditional concrete (TC). Since the transport properties of concrete are strongly depending on its pore structure, the question rises to what extent the gas permeability of SCC gets affected by the change in mixture design. In this paper the gas permeability of 16 mixtures SCC and 4 mixtures TC are being evaluated with special attention to the difference between SCC and TC, and the influence of the following parameters: water/cement ratio, powder content, type of filler, fineness of the filler, type of aggregate and cement/powder ratio. It was concluded that the gas permeability of SCC is about 5 times lower than the gas permeability of TC. The parameter with the largest impact on the gas permeability seems to be the water content and secondly the powder content. The capillary porosity has been estimated and a rather good correlation has been found with the gas permeability.      

Numerical simulation of self-consolidating concrete flow as a heterogeneous material in L-Box set-up: Effect of rheological parameters on flow performance

A computational fluid dynamics (CFD) software was used to simulate the effect of rheological parameters on the heterogeneous performance properties of self-consolidating concrete (SCC) in the horizontal and vertical directions of the L-Box set-up. These properties consist of flowability, blocking resistance, and dynamic segregation. Different suspending fluids having five plastic viscosity values (10–50 Pa.s), three yield stress values (14–75 Pa), two fluid densities (2000 and 2500 kg/m³), and two shear elasticity modulus values (100 and 1000 Pa) were considered. The suspensions consisted of a number of 135 in total spherical particles with 20-mm in diameter and 2500 kg/m³ density.The results of 25 simulations in total are found to correlate well with the rheological parameters of the suspending fluid. Plastic viscosity of the suspending fluid was shown to be the most dominant parameter affecting flow performance of SCC in the L-Box test. A new approach was also proposed to classify SCC mixtures based on the filling ability properties.     

Measurement systems for determining formwork pressure of highly-flowable concrete

This paper offers recommendations regarding test set-ups and measurement systems that can be used for laboratory evaluation and field testing of lateral pressure exerted by flowable concrete and self-consolidating concrete (SCC). Test results indicate that pressure sensors placed flush with the inner surface of the formwork can be used to assess the lateral pressure exerted by plastic concrete. The pore-water pressure resulting from the fluid phase of concrete can be evaluated using pore-water pressure sensors similar to the ones employed in soil mechanics. The sensors can be attached at different heights onto rigid formwork system to monitor changes in pressure with time.Sono-tubes made of cardboard are found not to be suitable for monitoring concrete pressure variations because of their flexibility which leads to erroneous values. A pressure column was developed to evaluate lateral pressure and its variations with time exerted by fresh SCC for heights of up to 10 m. Another system consisting of strain gages welded onto steel anchored bars inserted in the formwork was tested and compared to the pressure transducers system.     

Effect of steel fiber hybridization on the fracture behavior of self-consolidating concretes

In the present work the effect of steel fiber hybridization on the mechanical and rheological behavior of self-consolidating concretes was studied. Straight and hooked end steel fibers with different lengths and diameters were used as reinforcement in fiber volume fractions of 1.0% and 1.5%. The viscosity and shear yield stress of the concretes was determined using a parallel plate rheometer. The mechanical behavior was determined by means of compression, tension and bending tests. The movement of the neutral axis under bending load was experimentally determined by strain-gages attached to compression and tensile surfaces. The mechanical response of the material under bi-axial bending was addressed using the round panel test in three different boundary conditions. The obtained results indicated that the fiber hybridization improved the behavior of the composites for low strain and displacement levels increasing the serviceability limit state of the same through the control of the crack width.     

氯盐环境下混凝土耐久性研究进展

氯盐环境下混凝土结构的耐久性是沿海地区混凝土结构的一项关键指标,直接影响其正常使用寿命。从环境、材料、构件及结构4个层次系统论述了氯盐环境下混凝土耐久性的研究成果。分析认为当前的研究成果仍无法直接应用到实际工程中,还需继续研究。氯离子侵蚀环境和试件本身的受力状态应作为今后研究重点考虑的因素。     

混凝土结构耐久性的研究综述

混凝土是当今重要的结构工程材料,混凝土结构的耐久性问题日益突出.介绍了国内外混凝土结构耐久性研究概况以及主要研究内容,简述了混凝土结构耐久性的影响因素及相应的提高措施,同时提出了关于混凝土结构耐久性的未来发展趋势,为目前我国混凝土结构耐久性设计、施工和管理提供参考.     

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 30 m 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.     

State-of-the-art report on use of nano-materials in concrete

Nanotechnology application to concrete presents an innovative approach to improve concrete properties based on the ability to manipulate the cementitious material at an atomic scale. This paper presents a review of the nano-materials that have been used in concrete. The literature survey revealed that four nano-materials are most often used to modify concrete properties; these include nano-silica (nano-SiO₂), nano-titanium dioxide (nano-TiO₂), carbon nano-tubes (CNTs) and carbon nano-fibres (CNFs). All of these four nano-materials have shown improvement in many concrete properties. Both nano-TiO₂ and nano-SiO₂ reduce bleeding and segregation, and improve mechanical and transport properties. CNFs and CNTs tend to adversely affect the fresh properties due to agglomerations, which are overcome when a surfactant or ultrasonic mixer is used. However, both CNFs and CNTs significantly improve the mechanical properties of concrete. This paper also discusses how concrete durability is improved when nano-materials are added to concrete. In addition, this paper identifies several research needs based on the gaps in the current state of knowledge on using nano-materials in concrete.