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International Concrete Abstracts Portal

Showing 1-5 of 30 Abstracts search results

Document: 

20-207

Date: 

May 1, 2021

Author(s):

Lihe Zhang, Dudley R. Morgan, Iain Kirk, Anastasia Rolland, and Robert Karchewski

Publication:

Materials Journal

Volume:

118

Issue:

3

Abstract:

Wet-mix shotcrete has been used more and more for structural applications in the past few decades. Recently, wet-mix shotcrete was successfully used to construct a mass structural wall with congested reinforcement and minimum dimensions of 1.0 m in a sewage treatment plant. A low-heat shotcrete mixture that included up to 40% slag was proposed for shotcrete application. A preconstruction mockup was shot to established proper work procedures for shotcrete application and qualify the shotcrete mixture and shotcrete nozzlemen. Extraction of cores and cut windows from the mockup confirmed proper consolidation around the congested reinforcement. A thermal control plan was developed, which included laboratory and field testing requirements, thermal analysis modeling with a three-dimensional (3-D) finite element program, and thermal control requirements, including installation of cooling pipes and thermal blankets. Shotcrete proved to be an efficient means for mass concrete structural construction. Thermal control for mass shotcrete construction was studied, and the proposed thermal control plan was proved to function properly. The general guidance for mass shotcrete construction is provided.

DOI:

10.14359/51730423


Document: 

18-301

Date: 

March 1, 2021

Author(s):

Erik Stefan Bernard

Publication:

Materials Journal

Volume:

118

Issue:

2

Abstract:

It is well known that creep can affect the serviceability of concrete structures, including tunnel linings made using fiber-reinforced shotcrete (FRS). However, the possible effect of creep on the strength of structures is seldom explicitly considered in design. For cracked FRS loaded in tension or flexure, creep rupture of the fiber-concrete composite, either by pullout or rupture of fibers, can lead to structural collapse, at least when no alternative load path exists. In the present investigation, the influence of fiber geometry and surface roughness on creep rupture (expressed as the time-to- collapse) of FRS panel specimens subjected to a sustained flexural-tensile load has been assessed. The results suggest that geometric aspects of fiber design influence the propensity of the fiber composite to suffer creep rupture at a crack, and that collapse primarily occurs as a result of fiber pullout rather than tertiary creep of individual fibers. For the fibers presently investigated, geometric aspects of fiber design appear to exert a greater influence on creep rupture of the fiber composite than the properties of the material comprising the fibers.

DOI:

10.14359/51730410


Document: 

19-320

Date: 

July 1, 2020

Author(s):

Bruce Menu, Thomas Jacob-Vaillancourt, Marc Jolin, and Benoit Bissonnette

Publication:

Materials Journal

Volume:

117

Issue:

4

Abstract:

The experimental program reported in this paper sought to evaluate the efficiency of a range of curing methods in view of minimizing the evaporation rate at the surface of freshly placed shotcrete and preventing the detrimental consequences of early-age shrinkage. CSA A23.1-14 states that severe drying conditions should be considered to exist when the surface moisture evaporation rate exceeds 0.50 kg/m2/h (0.1 lb/ft2/h). In fact, the environmental conditions that lead to such evaporation rates are regularly experienced on construction sites, requiring that adequate protection of the concrete surface be carried out in a timely manner after placement. This research effort is aimed at quantifying the influence of selected curing methods upon the early-age moisture loss and the resulting shrinkage. The results show that early-age volume change of freshly sprayed shotcrete can be significantly reduced by adequate surface protection. Among the investigated methods, moist curing is found to be the most effective.

DOI:

10.14359/51724624


Document: 

15-268

Date: 

May 1, 2016

Author(s):

Lihe Zhang, Dudley Morgan, and Sidney Mindess

Publication:

Materials Journal

Volume:

113

Issue:

3

Abstract:

The question is sometimes asked: “How does the durability of shotcrete compare to that of cast-in-place concrete?” The durability of shotcrete and concrete structures is strongly influenced by their transport properties. While considerable data are available regarding the transport properties of cast-in-place concrete, little has been published concerning shotcrete transport properties. This study is directed at addressing this deficiency so that factual data are made available regarding the comparative transport properties of both wet, and dry-mix shotcretes and comparable cast-in-place concretes. In this study, a comparative evaluation was conducted on cast-in-place concrete; cast wet-mix shotcrete; sprayed wet-mix shotcrete; and sprayed dry-mix shotcrete in mixtures with and without fly ash, silica fume, and accelerators. Plastic concrete and wet-mix shotcrete tests conducted included slump, air content, and setting time. Hardened concrete and shotcrete tests conducted included compressive strength at 7 and 28 days; ASTM C642 boiled absorption and volume of permeable voids; ASTM C1202 rapid chloride permeability (RCP); ASTM C1792 rate of water absorption; and U.S. Navy specification UFGS 03 31 29-3 (chloride permeability test). Calculated transport property values compared included boiled absorption (BA) and volume of permeable voids (VPV), Coulomb values in RCP test, coefficient of diffusion (Diff[OH–]), effective coefficient of diffusion (Diff[OH–] x VPV), permeability (k) and tortuosity, in U.S. Navy specification UFGS 03 31 29-3 tests. This study demonstrates that properly applied wet-mix and dry-mix shotcretes can provide equivalent or superior transport properties (for example, ionic diffusion and permeability), and hence durability, to cast-in-place concrete.

DOI:

10.14359/51688829


Document: 

110-M45

Date: 

September 1, 2013

Author(s):

Yi-Wei Lin, Allan Scott, Liam Wotherspoon, and Jason M. Ingham

Publication:

Materials Journal

Volume:

110

Issue:

5

Abstract:

Engineered cementitious composite (ECC) shotcrete is a sprayable cement composite reinforced with synthetic fibers that exhibits a strain-hardening characteristic under tension. The ductile behavior of ECC makes it an ideal repair material for concrete structures as tensile strains from expansion of the original concrete structure can be accommodated. The aim of the reported research was to develop an ECC mixture design having superior durability properties while exhibiting a strain-hardening characteristic. Six mixture designs of ECC and a 5800 psi (40 MPa) cast-inplace concrete were tested using four test methods to determine their chloride resistance. Results from bulk diffusion testing showed that the most effective ECC mixture design, which incorporated a metallic soap additive, showed a 90% reduction in the chloride diffusion coefficient when compared with a 5800 psi (40 MPa) cast-in-place concrete. The alternating current (AC) resistivity, void, and sorptivity tests conducted did not show a strong correlation to the bulk diffusion test.

DOI:

10.14359/51685901


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