An evaluation of repair mortars installed by worm-pump spraying

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

2002

Materials and structures, 2005

Magazine of Concrete Research, 2000

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 mortars. Seven commercially available pre-packaged repair mortars were pumped and sprayed through a worm pump, three through a piston pump and two through a dry spray machine. A laboratory designed mortar was also worm and piston pumped. The properties measured included compressive and flexural strength, tensile bond strength, hardened density, modulus of elasticity, air permeability, sorptivity and drying and restrained shrinkage. In-situ test specimens were extracted from 500mmx500mmx100mm deep sprayed panels. Tests were also conducted on corresponding cast specimens and, where possible, on specimens that had been sprayed directly into a cube or beam mould. A new test to quantify the degree of reinforcement encasement has been developed and an initial investigation into the measurement of the restrained shrinkage of in-situ repairs is presented. The compressive and flexural strengths of the laboratory mix were comparable with the best of the commercially available preblended mortars. The values for modulus of elasticity, when compared with the compressive strength, were lower than published formulas for this relationship would suggest, especially at lower strengths.

2000

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 mortars. Seven commercially available prepackaged repair mortars were pumped and sprayed through a worm pump, three through a piston pump and two through a dry spray machine. A laboratory designed mortar was also worm and piston pumped. The properties measured included compressive and flexural strength, tensile bond strength, hardened density, modulus of elasticity, air permeability, sorptivity and drying and restrained shrinkage. In-situ test specimens were extracted from 500mmx500mmx100mm deep sprayed panels. Tests were also conducted on corresponding cast specimens and, where possible, on specimens that had been sprayed directly into a cube or beam mould. A new test to quantify the degree of reinforcement encasement has been developed and an initial investigation into the measurement of the restrained shrinkage of in-situ repairs is presented. The compressive and flexural strengths of the laboratory mix were comparable with the best of the commercially available preblended mortars. The values for modulus of elasticity, when compared with the compressive strength, were lower than published formulas for this relationship would suggest, especially at lower strengths. The air permeability of most of the mortars was lower than that for normal wet-cured concrete and decreased with an increase in compressive strength. The sorptivity values showed no clear relationship with the compressive strength. The type of wet-process pump was found to have little effect on the insitu compressive and flexural strengths, but did affect the bond strength, although mainly due to the stream velocity and w/c ratio rather than the pumping process. The pump type also effected the reinforcement encasement with higher stream velocities producing better encasement. 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.

… of Dundee, Scotland, UK on 8 …, 1999

1996

This research project has proved to be unique in both its focus and scope, and has produced a substantial array of knowledge and performance data for wet process sprayed mortars/concretes for repair.

1999

2009

This paper describes the activities of the International Tunnelling and Underground Space Association (ITA) Working Group 12 on Sprayed Concrete Use. The Working Group has carried out tasks with the purpose of promoting information exchange between National Groups and planning, coordinating and releasing the results of testing programs in order to advance the state-of-the-art of sprayed concrete use for underground support. The intention of the Working Group is to explore and develop the idea that the rational use of sprayed concrete improves possibilities for design and construction of new underground works.

2000

Sprayed concrete is a unique construction material that is ideally suited to the repair of concrete, brick and masonry structures. Repairing with sprayed concrete is attractive because of the flexibility of the application process and the elimination of formwork, but nearly all sprayed concrete repair projects in the UK are currently carried out by the dry process. The wet process has become dominant for largescale tunnelling applications involving robot-controlled spraying (eg in Scandinavia and more recently in the UK with ...