The influence of alkali-free and alkaline shotcrete accelerators within cement systems

Paglia, Christian; Wombacher, F; Böhni, H.

doi:10.1016/s0008-8846(01)00509-9

Cited by 121 publications

(27 citation statements)

References 7 publications

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“…Jawed and Skalny (1978) reported that alkali carbonates or hydroxides lowered the Ca 2þ concentration in the liquid phase, prevented the formation of ettringite and therefore the gypsum effect in controlling the C 3 A hydration, thus causing a premature stiffening (due to massive formation of AFm phase throughout the paste (Tang and Gartner, 1988)). Paglia and Wombacher (2001) studied the effect on setting of alkaline accelerators (based on a concentrated alkali hydroxide solution) and connected cement setting with a fast precipitation of calcium hydroxide crystals. The results of this paper supports the last hypothesis also if the former is not excluded.…”

Section: Discussionmentioning

confidence: 99%

Effects of alkali metal hydroxides on alkali-free accelerators

Maltese¹,

Pistolesi²,

Bravo³

et al. 2011

Advances in Cement Research

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Alkali-free accelerators are relatively new admixtures which allow concrete to be projected onto the rock wall during tunnel excavation. This sprayed concrete layer acts as a consolidating shield avoiding the convergence (the tendency of the section to squeeze) or dangerous structural collapses. Their efficiency could be related to: cement class and its chemical composition; environmental conditions (humidity; temperature); concrete mix design. A loss of accelerator efficiency is extremely dangerous for workers' safety as sudden collapses of the sprayed material can occur. Only a few studies have been published on the effects of these factors on the accelerating properties of alkali-free accelerators. In the present study, the influence of alkali metals (sodium and potassium) on cement pastes to which different alkali-free accelerators had been added was studied. It was discovered that the higher the alkali content the worse was the accelerator performance. In order to elucidate this phenomenon an analytical investigation was carried out. This included morphological (environmental scanning electron microscopy -field emission gun), chemical (induced coupled plasma -atomic emission spectroscopy), crystal-chemical (X-ray powder diffraction) and physicalchemical (hydration temperature profile; thermogravimetry/differential scanning calorimetry) evaluations. The results revealed significant morphological and crystal chemical differences among the investigated samples.

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Section: Discussionmentioning

confidence: 99%

Effects of alkali metal hydroxides on alkali-free accelerators

Maltese¹,

Pistolesi²,

Bravo³

et al. 2011

Advances in Cement Research

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“…2 It was not until 1950 that the cause of cement allergy; water-soluble chromium, was discovered. Wet cement is an irritant because of its abrasive texture and marked alkalinity resulting from the addition of accelerators.…”

Section: Introductionmentioning

confidence: 99%

“…Plain cement has a pH of around 11, but the introduction of additives, including various accelerators, makes it even more alkaline. 2 It was not until 1950 that the cause of cement allergy; water-soluble chromium, was discovered. 3 Both chromium and cobalt are impurities found in the clay used to make cement and, interestingly, dual sensitivity to both substances often occurs.…”

Section: Introductionmentioning

confidence: 99%

Occupational allergic contact dermatitis to chromium from cement: Estimating the size of the problem in Australia

et al. 2014

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“…In addition, in the initial hydration stage, those ingredients produced in the solution such as Ca(OH) 2 , SO 4 2-, and Al 2 O 3 combine to produce high-sulfur calcium sulphoaluminate hydrate (ettringite) that is not only conducive to the development of early strength but also reduces the concentration of Ca(OH)2, thus facilitating the hydration of C3S. The produced calcium silicate hydrate gel interlaps to form crystals with the grid structure, thus boosting condensation [7][8][9][10][11][12][13][14][15][16].…”

Section: Composition Of Liquid Acceleratormentioning

confidence: 99%

Study on the effect of new type liquid accelerator on the performance of shotcrete

Zhang¹,

Li²,

Qin³

et al. 2017

Frattura Ed Integrità Strutturale

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Shotcrete is an essential preliminary support means in New Austrian Tunneling Method (NATM) construction and plays a very important role in controlling the stability of surrounding rock. The accelerator is a necessary admixture in shotcrete and its quality can greatly affect shotcrete performance. This paper proposes a new liquid accelerator characterized by short initial and final setting time, small dosage, and good adaptability to cement. Laboratory tests and field tests are conducted to verify the influence of this liquid accelerator on performance of shotcrete. Numerical simulation is carried out to study the strength growth of shotcrete with time and interaction between the strength and stress release of surrounding rock. The results show that the initial and final setting time of this liquid accelerator is 2 minutes and 4 minutes respectively. Its dosage is just 1.5% to 4% of the cement quantity. Adding this liquid accelerator can effectively improve the early strength and reduce the later strength loss of shotcrete, and therefore enhance the supporting effects of shotcrete on surrounding rock. In the field application, it is an ideal liquid accelerator for shotcrete, characterized by little resilience, no slurry shedding, and low dust.

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The influence of alkali-free and alkaline shotcrete accelerators within cement systems

Cited by 121 publications

References 7 publications

Effects of alkali metal hydroxides on alkali-free accelerators

Effects of alkali metal hydroxides on alkali-free accelerators

Occupational allergic contact dermatitis to chromium from cement: Estimating the size of the problem in Australia

Study on the effect of new type liquid accelerator on the performance of shotcrete

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