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Development of Laboratory Device to Simulate Roller-Compacted Concrete Placement

ACI Materials Journal, Mar/Apr 2008 by Filho, José Marques, Paulon, Vladimir A, Monteiro, Paulo J M, de Andrade, Walton Pacelli, Molin, Denise Dal

Presented in this paper are the results from a laboratory study of a device that simulates roller-compacted concrete placement. The laboratory setup uses a novel device that consolidates concrete layers, realistically simulating site conditions, including several curing conditions. Laboratory tests results were compared to field results obtained at the Dona Francisca Hydro Power Plant, Brazil. Statistical methods were then used to analyze the correlation between laboratory and field results.

Keywords: dams; roller-compacted concrete; testing.

INTRODUCTION

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Roller-compacted concrete (RCC) was a significant evolution in the construction of dams. The RCC construction method often requires a dry concrete mixture and several horizontal contraction joints. This unique methodology has raised doubts about the accuracy of conventional laboratory tests to characterize the concrete's workability parameters and the strength in the field. These facts, together with the inherent variability of the concrete materials at each site, demand the use of conservative concrete mixtures at the beginning of construction. Only as the construction proceeds and field results become available can the concrete mixture proportions be improved. This solution adds to the overall cost of the project as it does not permit an optimization of the concrete mixtures during the early stages of the project.

Concrete has been used as a construction material for dams since the last decades of the nineteenth century.1 The structural models, construction methods, and quality control are well established and have been successfully implemented, as demonstrated by several old dams still in operation. The development of RCC in the 1980s had a major impact in the construction of concrete dams due to the substantial improvement in the speed of placement and compaction.2-4 Due to very dry consistency of RCC, most of the traditional tests methods used to characterize concrete are not applicable. Several tests, such as using drilled cores or constructing experimental layers of RCC in the field, have been proposed; however, few laboratory tests were developed and had their validity verified in real field conditions.5 The concrete expert must have tools and methodologies (that is, accurate laboratory tests) that allow the proper selection of materials to obtain an economical mixture proportion that satisfies the design criteria of strength, durability, and constructibility. Often, for economical reasons, local materials are used that may not have an ideal shape or granulometric distribution.3 To overcome this problem, preliminary laboratory tests are performed, such as strength and density, to optimize the granulometry of the aggregate. These tests provide relevant information for the design of construction facilities at the site, and even for the design of dam. After the laboratory tests are performed, final adjustments are made by using materials obtained from the crushing plant at the site and analyzing the results obtained at fills near the site using actual equipment and construction labor.

Another important aspect of the RCC technology is the continued need to increase the understanding of the material behavior. Up to now, tests performed during construction have been relevant to the improvement of the concrete mixture, but other problems arise during the normal construction process because of the short time between placing concrete layers.3 In addition, field results can only be used after a large amount of concrete is placed, delaying the optimization of the mixture proportions. This paper presents a method that performs test fills in laboratory conditions that simulate the site conditions to study any influencing factors (such as cure, temperature, treatment of joints in RCC dams designs, and construction techniques). To calibrate and to verify this methodology, compressive strength results and density from the proposed laboratory test were compared with the results obtained from field tests conducted at Dona Francisca Power Plant Dam, Brazil.

RESEARCH SIGNIFICANCE

Present laboratory tests do not have the capacity to predict the behavior of RCC in field conditions. The RCC technology has been employed in many recent projects, yet there is no appropriate methodology to simulate the real placement and compaction processes to optimize the mixture proportions.

To address this issue, a large-scale laboratory device was developed to better simulate field conditions. This study first presents the laboratory results, which are then verified through field work.

DESCRIPTION OF NEW EQUIPMENT

The equipment was designed to simulate (in the laboratory) actual site conditions for RCC, including the commercial compaction equipment and cure processes. The apparatus is composed of a rail system on which the roller-compacting structure moves. In an area at the center of the rails there is a pit onto which a mold is fixed. The mold remains entirely below floor level. The apparatus (Fig. 1) basically comprises three systems: one for horizontal movement, another for vertical movement, and a third for load application, all of which are described in the following.

Development of Laboratory Device to Simulate Roller-Compacted Concrete Placement

ACI Materials Journal, Mar/Apr 2008 by Filho, José Marques, Paulon, Vladimir A, Monteiro, Paulo J M, de Andrade, Walton Pacelli, Molin, Denise Dal

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