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International Concrete Abstracts Portal

Showing 1-5 of 28 Abstracts search results

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


Document: 

107-M54

Date: 

September 1, 2010

Author(s):

Erik Stefan Bernard

Publication:

Materials Journal

Volume:

107

Issue:

5

Abstract:

To date, experience in underground construction has indicated that creep deformations in conventionally reinforced shotcrete and steel fiber-reinforced shotcrete (SFRS) are small once hardening beyond the initial few weeks of hydration has occurred. At the same time, shotcrete reinforced with macrosynthetic fibers has become well established as a means of ground support in mines. This type of fiber-reinforced shotcrete (FRS) has demonstrated an ability to deform in response to highly plastic ground and thereby control stability. However, debate has arisen about the merits of using shotcrete reinforced with macrosynthetic fibers in civil tunnel linings. In particular, concerns have been expressed about the magnitude of post-crack creep-related deflections likely in the long term. The present investigation was instigated to determine the relative magnitude of time-dependent post-crack deflections typical of shotcrete reinforced with macrosynthetic fibers and to compare this with SFRS tested under nominally identical conditions.

DOI:

10.14359/51663967


Document: 

101-M39

Date: 

September 1, 2004

Author(s):

Christian S. B. Paglia, Franz J. Wombacher, and Hans K. Bohni

Publication:

Materials Journal

Volume:

101

Issue:

5

Abstract:

The strength development of mixtures accelerated with alkali-free and alkaline admixtures is clarified. The alkali-free admixtures do not interfere with the calcium silicatehydrate gel development. A good dissolution of the admixture—for instance, the calciumsulfoaluminate-rich one—causes the ettringites to be homogeneously distributed within the cementitious mass, thus acting as a crack arrester and enhancing the strength. On the other hand, an inhomogeneous distribution of the admixture results in the formation of high voluminous ettringite enrichments that weaken the microstructure and result in the strength decrease of the alkali-free accelerated mixtures. The addition of the alkaline accelerator delays the hydration of the calciumsilicate components to calciumsilicatehydrate gel and its densifying process. Consequently, a general high porosity persists up to 6 months, resulting in the lowest strength among the accelerated mixtures.

DOI:

10.14359/13420


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