Low-volume wet-process sprayed concrete: pumping and spraying

Construction and Building Materials, 1996

The lack of durability of reinforced concrete structures often refers to the corrosion of the reinforcing steel and the subsequent spalling of the cover concrete. With the use of water sorptivity in quantifying the quality of concrete, this paper discusses the deficiencies in the common practice of specifying concrete for reinforcement protection. The paper also demonstrates how water sorptivitv can be used as a simole oerformance criterion for specifying durable concrete.

The aggregate portion of concrete mixtures and mixture production paradigms are discussed starting with work by D. A. Abrams, published in 1918, through projections for the 21st century. Past and current paradigms and the background for the paradigm shift that took place between the mid 1930s and 1970 are described. The reason for "old concrete" outperforming new concrete is explained. A graphic with five zones that can be correlated with combined aggregate grading is provided as a means to evaluate mixtures and project performance. A second paradigm shift, started in 1986, is discussed. It has led to changes in ASTM, ACI, some state DOT, and USAF standards. Premature distress of US Air Force airfields and problem resolution are described and correlated with the current paradigm shift. When needed to support the subject, non-aggregate related matters are mentioned.

Materials and Structures, 2007

This paper, which reports on part of a three year research project into wet-process sprayed mortars and concretes for repair, investigates the hardened performance of wet-process sprayed fine concretes. It follows on from an earlier paper by the authors on the performance of hardened wet-process sprayed mortars and some comparisons with these are made here 1. Work has also been completed by the authors on the pumping and rheology of the fine concrete mixes presented here 2. Nine laboratory-designed fine concretes were pumped and sprayed through a wetprocess piston pump and one through a dry-process pump. The properties measured included compressive and flexural strength, tensile bond strength, hardened density, elastic modulus, sorptivity and drying and restrained shrinkage. Insitu test specimens were extracted from 500x500x100mm deep sprayed panels. Hardened property tests were also conducted on corresponding cast specimens and, where possible, on specimens that had been sprayed directly into a cube or beam mould. The compressive strengths of the cast cubes, although very similar, were usually slightly greater than the in-situ cubes, the opposite of what was found for wetsprayed mortars 1. Inconsistent results for compressive and flexural strengths obtained from spraying directly into a steel mould suggest that this method is not as reliable when using a piston pump as it is when using a low-output worm pump 1. The bond strength of all the mixes exceeded 2.1 MPa at 7 days. The values for modulus of elasticity, when compared with the compressive strength, were similar to published data for this relationship. The sorptivity values showed only a slight relationship with the compressive strength. The mixes exhibited a wide range of drying shrinkage, but the data from the restrained specimens suggest an actual repair is influenced as much by ambient conditions as it is by the mix proportions. Low-volume wet-process sprayed concrete: hardened properties Version 3 Chris Goodier

Cement and Concrete Composites, 2009

The modulus of elasticity is a fundamental parameter for the design of structures. It has been studied in the literature and several standards include equations to predict its value for conventional concrete regarding the compressive strength of the material. However, the same is not true in the case of sprayed concrete. This special concrete presents singular characteristics due to the spraying process that must be considered in the prediction of this property. The objective of the present communication is to perform an analysis of the modulus of elasticity of sprayed concrete. For that, an experimental program considering the mechanical properties of the material was executed. Furthermore, the applicability of formulations available in current codes and guidelines to estimate the modulus of elasticity of conventional concrete is assessed. The analysis conducted provides the basis to adapt the current formulations, taking into account the specificities of sprayed concrete: porosity and rebound. In this sense a semi-analytical expression is proposed.

1993

The late Robert E. Philleo served as a project consultant during the initial stage of the project. He helped in defining the criteria for high performance concrete and in setting the direction of the research. The research team benefited greatly from his guidance and many stimulating discussions. The research team also received valuable support, counsel, and guidance from the Expert Task Group (see cover 3 for a listing of ETG members). The support and encouragement provided by Inam Jawed, SHRP program manager, are deeply appreciated.

1993

This report presents a summary of each phase of a 4-year research program of the Strategic Highway Research Program (SHRP), which examined the mechanical behavior of high performance concretes. For each phase of the research, the objective, scope, results, and conclusions are summarized. The report covers the literature search and review, the development of mixture proportions of three categories of high performance concrete, the laboratory studies and field trials of the concretes, and the laboratory studies of high early strength fiber reinforced concrete. An assessment is made of how the research met its objectives and what the limitations in some of the research are. The report also suggests removing certain limitations in some of the current specifications that prevent the use of high performance concrete and concludes with a list of future research needs. Two technical guides on the production and use of high performance concrete, as well as two proposed specifications for tes...

ACI Materials Journal, 2013

The hazard rate function for concrete structures often is portrayed as a “bathtub”-shaped curve, with a finite ever-decreasing probability of early-age failures being followed by a life with a relative low, constant probability of failure that ultimately increases dramatically as the end of service is reached. Ideally, new concrete technologies should reduce the failures occurring at both ends of this service life spectrum. VERDiCT (Viscosity Enhancers Reducing Diffusion in Concrete Technology) is one such strategy, based upon increasing the pore solution viscosity. This approach has the potential to reduce the propensity for early-age cracking, while also reducing long-term transport coefficients of deleterious ions such as chlorides. In this paper, the performance of a typical VERDiCT admixture, a viscosity modifier/shrinkage-reducing admixture, is investigated in mortar and concrete, both as an addition to the mixing water and as a concentrated solution used to pre-wet fine lightweight aggregates. A reduction in early-age cracking is achieved by eliminating autogenous shrinkage stresses that typically develop in lower water-to-cementitious materials ratio concrete. By substantially increasing the viscosity of the pore solution in the concrete, the resistance to ionic diffusion is proportionally increased relative to a control concrete without the VERDiCT admixture. Here, chloride ion diffusion coefficients are evaluated for two types of concrete containing typical substitution levels of supplementary cementitious materials, namely either 25 % fly ash or 40 % slag by mass. For the eight concrete mixtures investigated, the effective diffusion coefficient was reduced by approximately 33 % by adding the VERDiCT admixture, which, in practice, may imply a 50 % increase in their service life, while the autogenous shrinkage was virtually eliminated. However, these benefits in early-age cracking resistance and long-term durability are tempered by up to a 20 % reduction in compressive strength that may need to be accounted for at the design stage.

Advanced Cement Based Materials, 1996