Durable fiber reinforced self-compacting concrete

In order to produce thin precast elements, a self-compacting concrete was prepared. When manufacturing these elements, homogenously dispersed steel fibers instead of ordinary steel-reinforcing mesh were added to the concrete mixture at a dosage of 10% by mass of cement. An adequate concrete strength class was achieved with a water to cement ratio of 0.40. Compression and flexure tests were carried out to assess the safety of these thin concrete elements. Moreover, serviceability aspects were taken into consideration. Firstly, drying shrinkage tests were carried out in order to evaluate the contribution of steel fibers in counteracting the high concrete strains due to a low aggregate-cement ratio. Secondly, the resistance to freezing and thawing cycles was investigated on concrete specimens in some cases superficially treated with a hydrophobic agent. Lastly, both carbonation and chloride penetration tests were carried out to assess durability behavior of this concrete mixture.     

A method for mix-design of fiber-reinforced self-compacting concrete

The addition of fibers to self-compacting concrete (SCC) may take advantage of its superior performance in the fresh state to achieve a more uniform dispersion of fibers, which is critical for a wider structural use of fiber-reinforced concrete. Some useful, mainly empirical, guidelines are available for mix design of fiber-reinforced SCC. In this work a “rheology of paste model” is applied to the mix design of Steel Fiber Reinforced SCC (SFRSCC). Fibers are included in the particle size distribution of the solid skeleton through the concept of an equivalent diameter, defined on the basis of the specific surface. The influence of fibers (type and quantity) on the grading of solid skeleton, minimum content and rheological properties of the paste required to achieve the required self-compactability and rheological stability were studied. Tests were conducted on both plain and fiber-reinforced concrete made with a variety of mix compositions. In addition, rheological tests were made with corresponding cement pastes.     

Parameter-study on the influence of steel fibers and coarse aggregate content on the fresh properties of self-compacting concrete

Self-compacting concrete (SCC) offers several economic and technical benefits; the use of steel fibers extends its possibilities. Steel fibers bridge cracks, retard their propagation, and improve several characteristics and properties of the concrete. Fibers are known to significantly affect the workability of concrete. Therefore, an investigation was performed to compare the properties of plain SCC and SCC reinforced with steel fibers. Two mixtures of SCC with different aggregate contents were used as reference. Each of the concretes was tested with four types of steel fibers at different contents in order to answer the question to what extent the workability of SCC is influenced. The slump flow, a fiber funnel and the J-ring test were used to evaluate the material characteristics of the fresh concrete. This paper discusses the suitability of the applied test methods and the effect of the coarse aggregate content, the content and type of steel fibers on the workability of SCC.     

Corrosion of steel fibre reinforced concrete from the cracks

The corrosion of steel fibres in the cracked section has been under investigation by many researchers since the last 15 years. It is reported widely that in case of steel fibres reinforced concrete (SFRC), corrosion is less active as compared with steel bars. In the cracked section, the durability of the material depends on the performance of the bridging capacity of the fibres embedded in the concrete. The corrosion of the fibres not only could produce the spalling of concrete but it could also reduce the sectional area of the fibres, turning the durability of structures in danger. This study focuses on those two aspects of fibre corrosion. The tests were performed on cracked SFRC samples with 0.5-mm crack mouth openings (CMOs) exposed to marine-like environment for 1 year. The results confirm the small sensitivity of SFRC to corrosion. Surprisingly, they made appear an increase of the flexural strength after corrosion. The factors affecting the corrosion of the fibres and the reasons for the increase in flexural strength after corrosion are discussed.     

Flow conditions of fresh mortar and concrete in different pipes

The variation in fresh concrete flow rate over the pipe cross section was investigated on differently coloured and highly flowable concrete mixes flowing through pipes of different materials (rubber, steel, acryl). First, uncoloured (gray) concrete was poured through the pipe and the pipe blocked. Similar but coloured (black) concrete was then poured into the pipe filled with gray concrete, flowing after the gray concrete for a while before being blocked and hardened. The advance of the colouring along the pipe wall (showing boundary flow rate) was observed on the moulded concrete surface appearing after removing the pipe from the hardened concrete. The shapes of the interfaces between uncoloured and coloured concrete (showing variation of flow rate over the pipe cross section) were observed on sawn surfaces of concrete half cylinders cut along the length axes of the concrete-filled pipe. Flow profiles over the pipe cross section were clearly seen with maximum flow rates near the centre of the pipe and low flow rate at the pipe wall (typically rubber pipe with reference concrete without silica fume and/or stabilizers). More plug-shaped profiles, with long slip layers and less variation of flow rate over the cross section, were also seen (typically in smooth acrylic pipes). Flow rate, amount of concrete sticking to the wall after flow and SEM-images of pipe surface roughness were observed, illustrating the problem of testing full scale pumping.     

The segregation tendency in the vibration of high fluidity concrete

The introduction of superplasticizer (Sp) has produced concrete that could flow easily under its own weight. In balancing the concrete's ability to flow at the same time maintaining the coarse aggregate distribution, the viscosity of concrete must be enhanced. This study aimed to investigate the effect of vibration on such flowable yet viscous concrete. Concrete flowability and viscosity are quantified by the standard slump cone and V-funnel test, respectively. Despite being flowable, the study concluded that concrete viscosity is an important parameter in determining the tendency for coarse aggregates to segregate. Large-sized coarse aggregates are affected more by the vibration process than the small-sized ones.     

A study on the applicability of vibration in fresh high fluidity concrete

The introduction of superplasticizers (Sp) in the production of concrete has produced highly flowable mixtures with enhanced viscosity. In cases of optimum flowability and viscosity, for example self-compacting concrete (SCC), no vibration is necessary for placement. However, such ideal conditions are not practically easy to achieve and deviations are possible. This paper reviews the results of a study to investigate the vibration of such high fluidity concrete. Two criteria were used to characterize the fresh mix, that is, slump flow and V-funnel time (V-time). Firstly, the feasibility of vibration on such mixes was studied. Then, the significance of flowability and viscosity was determined. Next, the relationship between workability and its segregation tendency was investigated. Finally, concrete mixes that missed SCC criteria were vibrated. Three different scenarios of vibration were concluded: namely, mix that accept vibration freely, mix that required controlled vibration and mix that needed prior treatment of viscosity enhancing agent (VEA) before vibration.     

Reproportioning of steel fibre reinforced concrete mixes and their impact resistance

In this experimental investigation, a practical rapid method of proportioning steel fibre reinforced concrete (SFRC) mixes is developed and validated. The basis for developing this is to use the reproportioning method, which has already been developed for proportioning normal density cement concrete mixes, for SFRC mixes. Based on the results of the trial mix, two SFRC mixes having 28 day target strength of 30 and 50 MPa are designed using this technique and examined regarding its validation. In addition, the impact resistance of these reproportioned Plain Concrete (PC) and SFRC is studied at 7 and 28 days. It is observed that the SFRC has developed significant impact resistance even for a small addition of steel fibres. Pulse velocity test is conducted at different ages to assess the quality of concrete. It is found that all concrete specimens could be classified under good quality.     

From ordinary rhelogy concrete to self compacting concrete: A transition between frictional and hydrodynamic interactions

This paper focuses on the physical phenomena involved in the transition between ordinary fluidity concrete and high fluidity concrete according to the aggregate content of the mixture. It is shown that there exists a strong transition in the rheological behavior of concrete between a regime dominated by the friction between aggregate particles and a regime dominated by hydrodynamic interactions far less dissipative. It is also demonstrated that it is possible to define a transition criterion between these two regimes. Finally, the consequences of these changes in mix design on the mechanical strengths of the concretes are studied showing that a small decrease in granular skeleton volume fraction, which may generate a decrease in yield stress of almost two orders of magnitude, only reduces the mechanical strength of a few percents.     

Self-consolidating concrete incorporating new viscosity modifying admixtures

Self-consolidating concrete (SCC) is known for its excellent deformability, high resistance to segregation and use without applying vibration in congested reinforced concrete structures characterized by difficult casting conditions. The use of viscosity modifying admixtures (VMA) has proved very effective in stabilizing the rheology of SCC. Commercial VMAs currently available on the market are costly, which increases the cost of such a concrete. This article presents the suitability of four different types of new polysaccharide-based VMA in the development of SCC. A preliminary investigation was carried out on the rheological properties and setting times of mortar mixes with various types and dosages of VMA to study the influence and suitability of new VMAs. A more detailed study was then carried out on the SCC fresh and hardened properties such as slump flow, segregation, bleeding, flow time, setting time and compressive strength of different mixes with various dosages of an identified new VMA. The performance of various SCC mixtures with the new VMA was compared with a SCC using a commercial VMA designated as “COM” and a SCC mixture with Welan gum. The study on new VMA is encouraging and confirms the production of satisfactory SCC with acceptable fresh and hardened properties comparable with or even better than that made with commercial VMA and Welan gum. The suggested mix with 0.05% of the new Type A VMA satisfies the requirement of fresh and hardened properties of SCC and will require 7% less VMA dosage than that required in the commercial VMA mixture. The SCC with new VMA is also cost-effective.     

SCC formwork pressure: Influence of steel rebars

The formwork pressure exerted by a given Self Compacting Concrete (SCC) depends on its thixotropic behavior, on the casting rate and on the shape of the formwork. It can moreover be expected that, in the case of a formwork containing steel rebars, these should also play a role. In first part, the specific case of a cylindrical formwork containing a single cylindrical steel rebar is studied. In second part, a comparison of the theoretical predictions to the experimental measurements of the pressure drop, after the end of casting SCC, was determined and the proposed model was validated. Finally, an extrapolation is suggested of the proposed method to the case of a rectangular formwork containing a given horizontal section of steel rebars, which could allow the prediction of the formwork pressure during casting.     

Medium strength self-compacting concrete containing fly ash: Modelling using factorial experimental plans

Fresh self-compacting concrete (SCC) flows into place and around obstructions under its own weight to fill the formwork completely and self-compact, without any segregation and blocking. The elimination of the need for compaction leads to better quality concrete and substantial improvement of working conditions. SCC mixes generally have a much higher content of fine fillers, including cement, and produce excessively high compressive strength concrete, which narrows its field of application to special concrete only. To obtain maximum benefit from SCC, it has to be adopted in general concrete construction practice. Such practice requires inexpensive and medium strength concrete.This investigation aims to develop medium strength SCC (MS-SCC). The cost of materials will be decreased by reducing the cement content and by using pulverised fuel ash (PFA) with a minimum amount of superplasticizer (SP). A factorial design was carried out to mathematically model the influence of five key parameters on filling and passing abilities, segregation and compressive strength, which are important for the successful development of medium strength self-compacting concrete incorporating PFA. The parameters considered in the study were the contents of cement and PFA, water-to-powder (cement+PFA) ratio (W/P) and dosage of SP. The responses of the derived statistical models are slump flow, fluidity loss, Orimet time, V-funnel time, L-box, JRing combined to the Orimet, JRing combined to cone, rheological parameters, segregation and compressive strength at 7, 28 and 90 days. Twenty-one mixes were prepared to derive the statistical models, and five were used for the verification and the accuracy of the developed models. The models are valid for mixes made with 0.38 to 0.72 W/P, 60 to 216 kg/m³ of cement content, 183 to 317 kg/m³ of PFA and 0% to 1% of SP, by mass of powder. The influences of W/P, cement and PFA contents, and the dosage of SP were characterised and analysed using polynomial regression, which can identify the primary factors and their interactions on the measured properties. The results show tha MS-SCC can be achieved with a 28-day compressive strength of 30 to 35 MPa by using up to 210 kg/m³ of PFA.     

An integrated approach for modelling the tensile behaviour of steel fibre reinforced self-compacting concrete

The present work resumes the experimental and numerical research carried out for the development of a numerical tool able of simulating the tensile behaviour of steel fibre reinforced self-compacting concrete (SFRSCC). SFRSCC is assumed as a two phase material, where the nonlinear material behaviour of SCC matrix is modelled by a 3D smeared crack model, and steel fibres are assumed as embedded short cables distributed within the SCC matrix according to a Monte Carlo method. The internal forces in the steel fibres are obtained from the stress–slip laws derived from the executed fibre pullout tests. The performance of this numerical strategy was appraised by simulating the tensile tests carried out. The numerical simulations showed a good agreement with the experimental results.     

Permeation properties of self-compacting concrete

Permeation properties, which include permeability, absorption, diffusivity etc., have been widely used to quantify durability characteristics of concrete. This paper presents an experimental study on permeation properties of a range of different self-compacting concrete (SCC) mixes in comparison with those of selected traditional vibrated reference (REF) concretes of the same strength grade. The SCC mixes with characteristic cube strength of 40 and 60 MPa were designed containing either additional powder as filler or containing no filler but using a viscosity agent. The results indicated that the SCC mixes had significantly lower oxygen permeability and sorptivity than the vibrated normal reference concretes of the same strength grades. The chloride diffusivity, however, appeared to be much dependent on the type of filler used; the SCC mixes containing no additional powder but using a viscosity agent were found to have considerably higher diffusivity than the reference mixes and the other SCCs.     

Relationship between the Bingham parameters and slump

Viscometers in general have never been particularly popular at the jobsite. They are however well suited at the laboratory as they measure concrete consistency in terms of fundamental physical quantity, known as the yield stress and plastic viscosity. In contrast to viscometers, the slump cone is by far the most accepted tool for measuring consistency at the jobsite. This is due to its simplicity in handling. With the significance of both types of devices, it is clearly important to relate them to each other. The result of this study suggests a relationship between the yield stress and slump that depends on the concrete mixture proportions. More precisely, a particular trend line between the yield stress and slump seems to depend on volume fraction of matrix used in the concrete. The study shows a low correlation between the slump and plastic viscosity.     

Distinct-layer casting of SCC: The mechanical consequences of thixotropy

It is demonstrated in this paper that thixotropic behavior of Self Compacting Concrete (SCC) may induce, in specific conditions, distinct-layer casting of the material that can generate lowered mechanical resistances in the final structure. First, the distinct-layer casting phenomenon is defined and described along with its potential consequences. Then, experimental results obtained for various SCC show that there exists a critical delay between layers casting above which separated layers are created in the element and generate losses of mechanical strength. This critical delay depends strongly on the thixotropic behavior of the SCC, the thickness of the layers and on the roughness of the interface between the two layers. Finally, an analytical method allowing for a rough prediction of this critical delay is proposed.     

Comparative evaluation of steel mesh, steel fibre and high-performance polypropylene fibre reinforced shotcrete in panel test

In this study, experimental investigations were performed on steel mesh (SM), steel fibre (SF) and high-performance polypropylene fibre (HPPF) reinforced shotcrete (HPPFRS) panels to evaluate performance characteristics such as toughness, flexural ductility, energy absorption and load capacity. The panel tests, in accordance with European specification for sprayed concrete (EFNARC), were made on 18 prismatic specimens having the same mix designs and were cured for 28 days but reinforced with various fibres. In addition, the rebound characteristics of these mixes were determined to compare the actual in situ fibre contents.Test results show that all reinforcements, including HPPFs that are low-modulus fibres, greatly improved the flexural ductility, toughness, and load-carrying capacity of the brittle matrix. It was seen that there was a positive synergy effect between steel and polypropylene fibre in hybrid fibre usage from a performance point of view. According to results, it can be concluded that a hybrid polypropylene-SF can be used alternatively instead of SM and monosteel fibre as a reinforcement in shotcrete applications to get better efficiency in mechanical properties of composite.     

A generalized approach for the determination of yield stress by slump and slump flow

The slump test (ASTM C-143) is the most common method for assessing the flow properties of fresh concrete. Although slump provides a qualitative measure of workability, the relationship between slump and more quantitative rheological parameters is not fully understood. In this study, a dimensionless model relating slump to yield stress is further developed and generalized as a function of cone geometry. Yield stress measurements of cement paste are performed using a vane technique and compared with slump measurements using cylindrical and conical geometries. The cylindrical slump model is in excellent agreement with the experimental yield stress data obtained using the vane method. The data for the conical slump measurements fit the cylindrical model at low yield stress values, but the results deviate as the yield stress of the paste increases. Most of the other slump models available in the literature, including finite element models, predict the same yield stress for a given slump when converted to dimensionless form. The results suggest that a fundamental relationship exists between yield stress and slump that is independent of the material under investigation and largely independent of cone geometry.     

Correlation between L-box test and rheological parameters of a homogeneous yield stress fluid

In this paper, a theoretical analysis of the L-box test is proposed in the case where no heterogeneity is induced by the flow. It is first demonstrated that if the standard procedure is followed and the L-box gate promptly lifted, the flow is dominated by inertia effects, depending on the lifting speed of the gate and thus on the operator. When the gate is slowly lifted, the flow and flow stoppage of a homogeneous yield stress fluid in a bounded channel are first studied. The obtained theoretical shape of the sample at stoppage is successfully correlated to the experimental results in the case of limestone powder suspensions. Then, the influence of steel bars was included in both the theoretical and the experimental study. Finally, practical applications of the present work to the case of real self-compacting concrete are suggested.     

Relation between fibre distribution and post-cracking behaviour in steel fibre reinforced self-compacting concrete panels

In this research, the influence of the fibre distribution and orientation on the post-cracking behaviour of steel fibre reinforced self-compacting concrete (SFRSCC) panels was studied. To perform this evaluation, SFRSCC panels were cast from their centre point. For each SFRSCC panel, cylindrical specimens were extracted and notched either parallel or perpendicular to the concrete flow direction, in order to evaluate the influence of fibre dispersion and orientation on the tensile performance. The post-cracking behaviour was assessed by both splitting tensile tests and uniaxial tensile tests. To assess the fibre density and orientation through the panels, an image analysis technique was employed across cut planes on each tested specimen. It is found that the splitting tensile test overestimates the post-cracking parameters. Specimens with notched plane parallel to the concrete flow direction show considerable higher post-cracking strength than specimens with notched plane perpendicular to the flow direction.