Workability Control Research Articles

Impact of physical and physicochemical properties of supplementary cementitious materials on structural build-up of cement-based pastes

Understanding the structural build-up is relevant to new technologies that require workability control, such as 3D concrete printing. The effect of supplementary cementitious materials (SCM) particle size (i.e. specific surface area and particle density) and physicochemical behavior (i.e., chemical reactivity and surface potential) and their interactions with the primary mixture parameters (i.e., water to cement ratio, cement reactivity and SCM replacement) on the structural build up of cementitious paste were studied. The growth of static yield stress with time was used to characterize the structural build up of cementitious pastes. Calorimetric curves were also measured. Results showed that the effect of SCM on structural build up is governed by their particle density and surface potential. The structural build up can be raised by increasing the number of contact points (governed by particle density and w/c), the growth rate of C-S-H bridges (governed by surface potential), or the reactivity of cement.

Development of multifunctional plaster using nano-TiO2 and distinct particle size cellulose fibers

The present study reports on the development of multifunctional plaster showing superior thermal insulation, ability to control the indoor RH and NOx photocatalytic degradation. The plaster contains TiO2 nanoparticles (1wt.%) and 0–4wt.% fibers of two distinct sizes: 1mm<d<2mm (Fb1-2mm) and 2mm<d<4mm (Fb2-4mm). The formulations were adjusted based on flow table and rheometer tests, aiming to assure a desirable workability. Plasters with similar workability (spread on table) showed distinct yield stress values over time and Fb(1-2mm) plays an important role on the workability control. Rheological behaviour was governed by Fb(2-4mm). Binary mixture 2.0Fb1-2mm + 2.0Fb2-4mm2·0Fb2-4mm required less water amount to show the same workability of the single formulation 4.0Fb1-2mm. However, the control of the rheological behavior over time was found difficult. The apparent porosity, water absorption and capillary index were strongly incremented with the rise of cellulose fiber concentration. Singular and binary samples present similar results and no significant differences were observed by changing the fibers size. Plaster’s buffering capacity and NOx uptake was considerably improved by using cellulose fibers, being this increment primarily governed by the fiber concentration. Formulation containing 4.0wt.% Fb(2-4mm) revealed the optimal performance.

Optimized workability and mechanical properties of FRCM by using fiber factor approach: theoretical and experimental study

This paper discusses a study on the optimization of mechanical properties of polypropylene fiber reinforced cementitious material (FRCM) through workability control of fresh properties. To this aim, a simple model is proposed herein describing the contact network between fibers inside FRCMs. The suspension was regarded as a two-phase composite in which fibers were suspended in a viscous cement paste. The theoretical framework presented in this paper and confirmed by experiments shows that there is a critical fiber factor above which the workability properties of fibers are mainly affected by the interactions of fibers in suspension. Moreover, there is a dense fiber factor above which the fibers tend to clump and both workability and mechanical properties of fibers significantly degrade. The obtained results show that adequate workability and a properly adjusted fiber factor are keys to obtain proper flexural and tensile strength. The findings in this paper can provide a rational foundation for mix design of FRCM by adjusting the fiber factor as an effective tool to control the workability of FRCM and practically achieve optimal hardened properties.

Prefabricated mud wall units based on a traditional Japanese building system: Lateral in-plane performance in terms of connection, and crack development using digital speckle photography

Abstract A shear wall composed by prefabricated mud wall units (PMWU) was studied. Mud panels reinforced by bamboo laths are enclosed in wooden frame, combining mud material’s high energy absorption and stiffness of wooden frame. Among the advantages are workability and quality control before and after assembly. The PMWU’s performance related to the number of frames’ connectors was analyzed. Digital speckle photography (DSP) was used to measure strains and finite element method (FEM) to validate the results. The shear stiffness of PMWU varied due to rotation of the panels. The stress transmission was influenced by the number of connectors via shear and contact between frames.

Compressive strength and modulus of elasticity of freshly compressed concrete

This paper is going to offer an interesting solution to enhance the compressive behavior of concrete in terms of strength and modulus of elasticity. In the presented method, by compressing the fresh concrete in a fabricated pressure apparatus, the excess water of concrete is expelled and the percent void is remarkably decreased. Applying this technique without needing the additive materials, external vibration and workability control, a significant enhancement in the strength and modulus of elasticity of the freshly compressed concrete (FCC) is observed. A parametric study is conducted to investigate the effect of various reference concrete (RC) strengths, different pressure levels and pressure duration on the behavior of FCC. Based on the regression analysis of the experimental data, this study provides empirical equations to predict the percentage increase in the compressive strength and modulus of elasticity of FCC specimens. A relationship between the modulus of elasticity and compressive strength for both the compressed and uncompressed concretes is statistically derived and then the results are compared with those calculated by the prediction models given in ACI 318, ACI 363 and EN 1992-1-1 codes. Finally, the code-compliant expressions for RC are modified for FCC.

Effect of metakaolin dispersion on the fresh and hardened state properties of concrete

The use of pozzolanic materials such as metakaolin in mortars and concretes is growing. Their use is usually related to the promotion of hydraulic binder reactions or to the mitigation of expansive reactions that can occur in concrete. Introduction of fine particles such as metakaolins, can have a strong effect on fresh and hardened state properties. This paper aims to study the effect of metakaolin in concrete formulations with a preset workability and to assess the system rheology but also its hardened state properties such as mechanical strength. The effect that the dispersion of metakaolin particles induces on concrete microstructure, particularly in porosity, is discussed. Formulations were prepared with several metakaolin amounts and workability was controlled either with water or a high range water reducer admixture (HRWRA). The use of HRWRA can cause deflocculation of metakaolin particles, allowing workability control in concrete and leading to better efficiency and improved performance.

Compressing fresh concrete technique and the effect of excess water content on physical–mechanical properties of compressed concrete

This paper offers an innovative practical technique for applications in which high workability concrete is needed. In this technique, concrete is produced by compressing the fresh concrete through a fabricated pressure apparatus without incorporating additives and no need for external vibration and workability control. Applying this technique, excess water is completely expelled out from the fresh concrete and porosity is remarkably decreased. In this study, several mixes having different excess water contents with the same cement and aggregates were prepared to attain different workability levels. To evaluate the effect of excess water content on properties of hardened concrete, the physical and mechanical properties of both compressed and uncompressed concrete were determined, including compressive strength, modulus of elasticity, strain at peak stress, stress–strain curve, failure mode, water absorption, density and ultrasonic pulse velocity. The results obtained from this study showed that the excess water content added to the fresh concrete does not influence the physical–mechanical properties of the compressed concrete while those of the uncompressed concrete are significantly degraded. Moreover, compressing the fresh concrete dramatically improves the properties of the compressed concrete, as compared to the corresponding uncompressed concrete.

A NEW VISUALIZING BLADDER NECK PUNCH WITH HIGH FREQUENCY COAGULATION ELECTRODE ATTACHMENT

Since Guthrie in 1828 first accurately described its clinical and pathologic manifestations and ten years later Mercier devised such ingenious instruments for its cure (which no doubt would have survived had there been reliable means of accurate diagnosis such as the cystoscope), many procedures have been tried and many instruments devised by clinicians scattered over Europe and America for the relief of obstruction due to contracture of the bladder neck, often called median bar. Each has added something of value to the solution of the problem. Fundamentally Young's punch procedure seems the method that most nearly attains the objective. The addition, by McCarthy, of the accessories and refinements illustrated inAof the accompanying illustration make for maximum efficiency with easy workability and delicate control. Superb vision through a foroblique telescope coupled with the last word in construction, workmanship and improved materials, together with the ease by which the bleeding