Ahmed F. Omran

Inclined Plane Test to Evaluate Structural Buildup at Rest of Self-Consolidating Concrete

This article describes how concrete flow resistance increases after casting due to physical restructuring and cement hydration, thus affecting some key characteristics of the material, including segregation resistance, lateral pressure exerted on formwork, and bond between successive lifts. A systematic program was undertaken to evaluate the structural buildup of self-consolidating concrete (SCC) using a novel inclined plane method. The critical angle of the plane at the commencement of movement of the sheared material placed onto a roughened surface is used to determine static yield stress. Repetitive tests carried out on SCC indicate that the rate of structural buildup has a relative error of 7 to 9%, depending on thixotropic level and shear history. Comparisons carried out with 29 SCC mixtures of various compositions demonstrate that yield stress characteristics determined using the inclined plane method are comparable to those measured using a concrete rheometer (R2 = 0.82).

Effect of SCC Mixture Composition on Thixotropy and Formwork Pressure

High lateral pressure exerted on formwork systems by self-consolidating concrete (SCC) is one of the hindrances for using such highly flowable concrete in cast-in-place applications. Self-consolidating concrete is a complex system that can be made using a wide range of mixture proportioning and often incorporated various chemical admixtures and supplementary cementitious materials. The investigation of the effect of each material ingredient independently on lateral pressure of SCC is not a simple task. In this study, thixotropy is rather used to assess the effect of various mixture parameters on formwork pressure. Thixotropy is determined by the evaluation of the structural buildup at rest using a concrete rheometer and two field-oriented test methods (inclined plane and portable vane). Sherbrooke pressure device is employed to evaluate the maximum lateral pressure of SCC. The device receives 0.5 m of fresh concrete and pressurized with air to simulate 13 m of concrete casting at the required casting rate. A parametric study and full-factorial design approaches were employed to evaluate the effect of concrete consistency level, coarse aggregate content, sand-to-total aggregate ratio, paste volume, and nominal maximum size of aggregate on SCC thixotropy and formwork pressure. The investigation resulted in proposing statistical models to determine the effect of each of the modeled mixture parameters and their interaction on thixotropy and lateral pressure. Contour diagrams were established to compare the trade-off between the effects of the different mixture parameters on thixotropy and formwork pressure characteristics. DOI: 10.1061/(ASCE) MT.1943-5533.0000463.

Production of RCC Using Biomass Fly and Bottom Ashes: From Laboratory to Fieldwork

AbstractRoller-compacted concrete (RCC) is widely used as an economical and durable pavement to withstand heavy loads on large areas or logging roads. The use of by-products from the cogeneration p...

Feasibility of Using Biomass Fly and Bottom Ashes to Produce RCC and PCC

AbstractRoller-compacted concrete (RCC) and paver-compacted concrete (PCC) are widely used in mass concrete and pavement. Alternative supplementary cementitious materials (ASCM) can be used in RCC ...

Prediction of SCC Formwork Pressure in Full-Scale Elements

Various prediction models, based on experimental results to evaluate formwork pressure exerted by self-consolidating concrete were established based on extensive laboratory evaluation. The models are based on the measurements of the structural build-up of the concrete with rest time and placement characteristics of the concrete. The latter includes the rate of rise of the concrete in the formwork, concrete temperature, and minimum dimension of the formwork. This paper presents the results of two campaigns of field validation carried out at Sherbrooke, Quebec, and Skokie, Illinois, to validate the prediction models. The results confirm that the established models offer adequate prediction of form pressure exerted by self-consolidating concrete.

CHARACTERIZATION OF FIBER REINFORCED SELF-CONSOLIDATING MORTARS FOR USE IN PATCHING DAMAGED CONCRETE

THIS RESEARCH AIMS TO STUDY THE EFFECT OF SUPPLEMENTARY CEMENTITIOUS MATERIALS (SCMS) SUCH AS QUARRY DUST LIMESTONE (QDL) AND NATURAL POZZOLANA (NP) ON THE PERFORMANCE OF FIBER REINFORCED SELF-CONSOLIDATING REPAIR MORTARS (FR-SCRMS). BASED ON PREVIOUS OPTIMIZATION OF QDL AND NP REPLACEMENT RATIOS, TWO MORTAR MIXTURES INCORPORATING 10% QDL AND 20% NP AS CEMENT REPLACEMENTS WERE PREPARED. THE EVALUATION WAS BASED ON FRESH (SLUMP FLOW, FLOW TIME), HARDENED (COMPRESSIVE AND FLEXURAL STRENGTHS AND ADHERENCE TO OLD CONCRETE USING SLANT SHEAR TEST). IN ADDITION, THE INFLUENCE OF THREE CURING CONDITIONS, SIMILAR FROM THOSE NORMALLY ENCOUNTERED IN THE FIELD WAS EVALUATED ON THE COMPATIBILITY BETWEEN REPAIR MATERIALS AND SUBSTRATE, UNDER FLEXURAL STRENGTH TEST BY USING THIRD-POINT’S LOADING BEAM TEST METHOD. IT IS DEMONSTRATED THAT THE FR-SCRMS IS PROMISING TO BE USED IN REPAIR CONCRETE STRUCTURES CLASS R4 (EN 1504-3) WITHOUT REDUCING THE ADHESIVE STRENGTH.

Effect of Formwork Characteristics on SCC Lateral Pressure

AbstractLateral pressure exerted on vertical formwork by fresh self-consolidating concrete (SCC) controls its design. Several factors, including material properties, placement conditions, and formw...