Measurement of Workability of Fresh Concrete Using a Mixing Truck

The main objective of this study is to evaluate the workability of fresh portland cement concrete while it is still in the mixing truck by determining fundamental rheological parameters (plastic viscosity and yield stress). Nine concrete mixtures with different values of yield stress and plastic viscosity were tested in a concrete truck. The measurements made with the truck were based on the typical method of determining the flow behavior in a traditional fluid rheometer; that is, the shear rate in the mixing truck was swept from high to low by varying the rotation speed of the drum. The results of these experiments are discussed and compared with data provided by the ICAR rheometer, a portable rheometer designed for measuring concrete rheology. The test results indicate that the mixing truck equipment is sufficiently sensitive to detect differences in yield stress, slump, and plastic viscosity. However, the plastic viscosity determined by the truck measurement did not correlate with plastic viscosity as measured by the ICAR rheometer, while the yield stress determined by the truck measurement did correlate well with the measured slump and the ICAR rheometer resultsSuggestions are given on how to improve the mixing truck for better use as a rheometer.     

Fresh properties of self-compacting rubberized concrete incorporated with fly ash

Solid waste management is one of the major environmental concerns in all over the world. High amounts of waste tires are generated each year and utilization of this waste is a big problem from the aspects of disposal, environmental pollution, and health hazards. In the production of self-compacting concrete, the incorporation of waste tires as partial replacement of aggregates is very limited. However, the use of waste tires might join the characteristics of self-compacting concrete (high flowability, high mechanical strength, low porosity, etc.) with the tough behavior of the rubber phase, thus leading to be a building material with more versatile performances. Thus, in this study, the usability of untreated crumb rubber as a partial substitute of fine aggregates with and without fly ash in the application of self-compacting concretes was investigated experimentally. For this purpose, a water–cementitious material ratio (0.35), four designated crumb rubber contents (0, 5, 15, and 25% by fine aggregate volume), and four fly ash content (0, 20, 40, and 60%) were considered as experimental parameters. Test results indicated that use of crumb rubber (CR) without fly ash (FA) aggravated the fresh properties of self-compacting rubberized concretes (SCRC) (slump flow diameter, T₅₀ slump flow time, V-funnel flow time, L-box height ratio, initial and final setting times, and viscosity). However, the use of CR with FA amended the fresh properties of SCRC.     

Effect of the mix design on the robustness of fresh self-compacting concrete

Self-compacting concrete (SCC) has many advantages compared to vibrated concrete. A disadvantage is the lower robustness of fresh SCC. SCC is more sensitive to small changes in the mix design, material properties, and the applied production methods. In an experimental program, the influence of important mix design parameters on the robustness of SCC was studied. First, the influence of the paste volume and the water-to-powder volumetric ratio was investigated. Depending on the mechanisms providing stability in the mixture, different levels of impact were observed. When the yield stress is the main factor providing stability in the mixture, a change in the water content will mainly affect the yield stress, making the stability of the yield stress the most important factor determining the robustness of the mixture and can be improved by lowering the paste volume. Analogue, the sensitivity of the plastic viscosity is determining the robustness of mixtures in which mainly the plastic viscosity is providing stability. The robustness of such a mixture can be improved by increasing the water-to-powder volumetric ratio. The influence of two types of viscosity modifying agents (VMA's) on the robustness of fresh SCC was examined in a second stage. The two used VMA's (diutan gum and attapulgite clay) were especially effective in SCC mixtures having a high yield stress and a low plastic viscosity. In mixtures having a low yield stress and a high plastic viscosity, the inclusion of a VMA in the mix design resulted in a decrease of the robustness.     

Properties of self-compacting portland pozzolana and limestone blended cement concretes containing different replacement levels of slag

In order to reduce energy consumption and CO₂ emission, and increase production, cement manufacturers are blending or inter-grinding mineral additives such as slag, natural pozzolana, and limestone. This paper reports on the results of an experimental study on the production of self-compacting concrete (SCC) produced with portland cement (PC), portland pozzolana (PPC) and portland limestone (PLC) blended cements. Moreover, the effect of different replacement levels (0–45%) of ground granulated blast furnace slag (GGBFS) with the PPC, PLC, and PC cements on fresh properties (such as slump flow diameter, T ₅₀₀ slump flow time, V-funnel flow time, L-box height ratio, setting time, and viscosity) and hardened properties (such as compressive strength and ultrasonic pulse velocity) of self-compacting concretes are investigated. From the test results, it was found that it was possible to manufacture self-compacting concretes with PPC or PLC cements with comparable or superior performance to that of PC cement. Furthermore, the use of GGBFS in plain and especially blended cement self-compacting concrete production considerably enhanced the fresh characteristics of SCCs.     

Filling ability and plastic settlement of self-compacting concrete

The use of self-compacting concrete (SCC) facilitates the placing of concrete by eliminating the need for compaction by vibration. Given the highly flowable nature of such concrete, care is required to ensure excellent filling ability and adequate stability. This is especially important in deep structural members and wall clements where concrete can block the flow, segregate and exhibit bleeding and settlement which can result in local defects that can reduce mechanical properties, durability and quality of surface finish.This paper shows results of an investigation of fresh properties of self-compacting concrete, such as filling ability measured by slump flow and flow time (measured by Orimet) and plastic fresh settlement measured in a columin. The SCC mixes incorporated various combinations of fine inorganic powders and admixtures. The slump flow of all SCCs was greater than 580 mm and the time in which the slumping concrete reached 500 mm was less than 3 s. The flow time was less than 5 s. The results on SCCs were compared to a control mix. The compressive strength and splitting tensile strength of SCCs were also measured.The effects of water/powder ratio, slump and nature of the sand on the fresh settlement were also evaluated. The volume of coarse aggregate and the dosage of superplasticizer were kept constant. It can be concluded that the settlement of fresh self-compacting concrete increased with the increase in water/powder ratio and slump. The nature of sand influenced the maximum settlement.     

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.     

Development of self-compacting high and ultra high performance concretes with and without steel fibres

This paper describes the steps taken to develop self-compacting high and ultra high-performance concretes with and without steel fibres. For the self-compacting concrete mixes without steel fibres the fulfilment of flow and cohesiveness criteria are sufficient for the mix design. However, for the design of self-compacting concrete mixes with steel fibres it is found, as expected, that they must additionally meet the passing ability criterion. The plastic viscosity of the mixes with and without steel fibres has been estimated from the known plastic viscosity of the cement paste using simple micromechanical relations.     

Laboratory investigation of rheological properties and scaling resistance of air entrained self-consolidating concrete

An experimental investigation was undertaken to analyze the influence of various admixtures on the rheological properties and scaling resistance of self-consolidating concrete. Such concrete is intended for use as a repair material for filling highly restricted areas, such as forms with closely spaced reinforcing steel bars. Several self-consolidating concrete mixtures having slump flow of 550+50 mm were prepared with water-to-cement ratios varying between 0.35 and 0.41. The mixtures were cast with 0 and 3 percent silica fume, with and without air-entraining admixture. All concretes incorporated superplasticizer and viscosity-modifying admixture to enhance deformability and stability. Rheological parameters (yield value and plastic viscosity) were measured using a concrete viscometer. The air content, unit weight, and consistency were also determined. The consistency was assessed using the slump flow and L-Flow methods. Tests performed on hardened concrete included compressive strength at 28 days (ASTM C 39), scaling resistance (ASTM C 672), durability to freezing and thawing (ASTM C 666) and measurement of the air-void parameters (ASTM C 457). Relationship between the simple slump flow and yield value and plastic viscosity measurements determined using a concrete viscometer are also discussed. In general, the laboratory test results indicate that it is possible to produce a frost durable, self-consolidating concrete with low yield value and high plastic viscosity (for such fluid concrete) which can be use as a repair material to fill highly restricted areas.     

Validation of BTRHEOM,the new rheometer for soft-to-fluid concrete

An investigation was performed on the objectivity of a new rheometer for soft-to-fluid concrete, called BTRHEOM. Firstly, the influence of concrete wall friction on the measurement of the Bingham constants was studied by finite-element simulations. It has been shown that this influence is limited, in particular on the measurement of shear yield stress. However, the quality of the estimate of plastic viscosity can be improved by applying a reduction of 10% to the bulk value. Secondly, a series of comparative tests was conducted with two other rheometers with different operating principles. The comparison with the intrinsic values as measured by a big coaxial-cylinder viscometer, the CEMAGREF-IMG rheometer, showed a satisfactory result for yield stress, but not for plastic viscosity, probably due to the segregation of the coarse aggregate in the CEMAGREF-IMG rheometer. For two concretes without segregation, the two rheometers yielded the same values. Another comparison with the LAFARGE rheometer (a modified version of Tattersall's two-point test) showed a good correlation between the measurements with the two instruments. Finally, the slump test was modelled by a simple numerical approach, from which a linear relation between slump and yield stress was derived. This relationship agrees with the experimental results.     

Simulating macroscopic behavior of self-compacting mixtures with DEM

Development of proper rheological models and suitable numerical methods are necessary for a thorough understanding of the basic flow properties of fresh mortar or concrete. Main challenge for models is to find a quantitative correlation between the model parameters and the properties and proportions of the mix ingredients. This paper presents a modeling approach for the rheological behavior of fresh self-compacting mixtures using a Discrete Element Method (DEM). The employed method is based on a conceptual idea where the grain-paste-grain interactions are explicitly described as an interactive two-phase paste-bridge system. Each mixture is considered to be an assembly of mutually interacting “grain-paste-grain” systems which can be characterized according to the mix composition with help of the “excess paste theory”. Macroscopic slump flow predictions are evaluated by laboratory tests. Simulations and experimental test results show good agreement.     

Rheology of fresh cement paste with superplasticizer and nanosilica admixtures studied by response surface methodology

Thirteen cement pastes, keeping the water/cement ratio constant at w/c = 0.30, with different amounts of two admixtures were prepared. A superplasticizer (modified polycarboxylic ether polymer) was studied in the range of 0.14–1.00% (over cement weight), while a viscosity-modifying admixture (nanosilica aqueous dispersion) was tested at 0.50–3.00% range (over cement weight). Oscillatory and steady shear rheometry, as well as results of modified slump test and Marsh funnel flow time of 13 formulations were evaluated by response surface methodology, in order to find the optimum recipe that reduces the viscosity while keeping the paste workability. It was predicted that a formulation with 0.39% w/w of superplasticizer and 2.78% w/w of viscosity-modifying admixture would provide a paste with a fifth of the viscosity of control (cement paste without any admixture), but with an acceptable slump. This formulation was prepared and tested, and the plastic viscosity was 1.00 Pa-s, while the oscillatory yield stress was 330 Pa. The admixtures did not affect the compression strength (48 MPa average, after 28 days), compared with the control.     

Rheological characterization of a time dependent fresh cement paste

Combining equilibrium and non-equilibrium rheological tests, the yield stress and the plastic viscosity corresponding to the completely build-up structure of a fresh cement paste have been determined. This experimental method is proposed to characterize time-dependent fluids because the values of these parameters are not dependent on the particular structural state of the system and, consequently, are not affected by the particular way in which the rheological test has been designed.     

Parameters influencing pressure during pumping of self-compacting concrete

The main difference between conventional vibrated concrete (CVC) and self-compacting concrete (SCC) is observed in the fresh state, as SCC has a significantly lower yield stress. On the other hand, the placement of SCC by means of pumping is done with the same equipment and following the same practical guidelines developed for CVC. It can be questioned whether the flow behaviour in pipes of SCC is different and whether the developed practical guidelines can still be applied. This paper describes the results of full-scale pumping tests carried out on several SCC mixtures. It shows primarily that the slump or yield stress of the concrete is no longer a dominating factor for SCC, as it is for CVC. Instead, the pressure losses are well related to the viscosity and the V-funnel flow time of SCC. Secondly, bends cause an additional pressure loss for SCC, which is in contrast to the observations of Kaplan and Chapdelaine and the estimation of the practical guidelines is not always on the safe side. Finally, due to the specific mix design of SCC, blocking is less likely to occur during pumping operations, but the same rules as for CVC must be applied during start-up.     

A two-phase composite materials approach to the workability of concrete

The present article is an attempt to establish basic composition-property relations for fresh concrete, using the two-phase composite materials approach and the law of plastic viscosity. Results of common practical tests of unit weight, slump test and Vebe test on systematic fresh concrete series, performed by the authors, are presented and are expressed through the following analytical models: the simple mixture rule for the unit weight: δ_c = δ_m + (δ_a − δ_m) V_a and the proposed plastic viscosity model for the workability tests: The slump test s_c = s_m The Vebe test T_m = T_m with good agreement. The indices m, a and c refer to the mortar, the aggregate, and the concrete, respectively, and V_a is the volume fraction of the coarse aggregate. The material constants M, k, and k′ depend on the characteristics of the mortar and the coarse aggregate phases. It is concluded that with the development of this analytical model a reasonable solution for the workability of fresh concrete has been obtained.     

Use of spent foundry sand and fly ash for the development of green self-consolidating concrete

In the United States alone, the foundry industry discards up to 10 million tons of sand each year, offering up a plentiful potential resource to replace sand in concrete products. However, because the use of spent foundry sand (SFS) is currently very limited in the concrete industry, this study investigates whether SFS can successfully be used as a sand replacement material in cost-effective, green, self-consolidating concrete (SCC). In the study, SCC mixtures were developed to be even more inexpensive and environmentally friendly by incorporating Portland cement with fly ash (FA). Tests done on SCC mixtures to determine fresh properties (slump flow diameter, slump flow time, V-funnel flow time, yield stress, and relative viscosity), compressive strength, drying shrinkage and transport properties (rapid chloride permeability and volume of permeable pores) show that replacing up to 100% of sand with SFS and up to 70% Portland cement with FA enables the manufacture of green, lower cost SCC mixtures with proper fresh, mechanical and durability properties. The beneficial effects of FA compensate for some possible detrimental effects of SFS.     

Influence of the rheological properties on the steel fibre distribution and orientation in self-compacting concrete

The interest in potential applications produced with self-compacting fibre reinforced concrete continues to grow, but in practice, problems associated with an uneven distribution and orientation of fibres in the concrete structure occur. It is not clear what exactly influences uneven distribution of fibres in self-compacting concrete (SCC) mixtures, especially during the casting and how different factors influence fibre orientation. The objective of this work was to investigate how rheological properties influence the steel fibre distribution in self-compacting concrete. This work also focuses on the investigation of steel fibre spatial orientation dependence on rheological properties of SCC, while keeping other casting parameters and the proportions of mixture components constant. Mixtures with three different rheological properties were chosen based on slump flow, slump flow time t₅₀₀ and static segregation values. The steel fibre orientation, volumetric concentration and spatial distribution values were determined in separate beam sections using three different non-destructive testing methods: electromagnetic induction, image analysis and computed tomography (CT scan). The comparison of the results is presented. The results show how different rheological properties of SCC affect the steel fibre orientation and distribution for the case of beams produced with the flow-induced casting method.     

The effect of viscosity modifying agents on mortar and concrete

The influence of different viscosity modifying agents (VMA) on the flow properties and the rheology of self-compacting mortars is studied. Additionally, their effect on the early hydration of cement pastes and on the development of concrete strength is determined. Beside the inorganic VMA microsilica (MS) and nanosilica slurry (NS) organic VMA based on high molecular ethylenoxide derivate (EO), natural polysaccharide (PS) and starch derivate (ST) are used. The different VMA are combined with a superplasticizer (SP).At constant water-to-binder ratio (w/b) the addition of VMA causes a decrease of mortar flow and an increase of flow time (V-funnel test). At the same time yield stress and plastic viscosity are increased. At a constant dosage of superplasticizer (SP) mixtures with VMA require a higher w/b to keep the same flow properties as the reference mixtures without VMA. In spite of the higher w/b flow time and plastic viscosity respectively are only slightly reduced. This property is especially beneficial for the production of stabilizer-type self-compacting concrete where the amount of fines can be reduced with the use of VMA. However, only the use of VMA PS and ST leads to smaller changes of flow when w/b is changed. The organic VMA show almost no influence on early cement hydration and the development of compressive strength. However, the inorganic VMA cause an acceleration of hydration and higher compressive strength at the age of 1 day.