Durability of concrete — Degradation phenomena involving detrimental chemical reactions

The term Ultra-High Performance Concrete (UHPC) refers to a relatively new class of advanced cementitious composite materials whose mechanical and durability properties far surpass those of conventional concrete. This class of concrete has been demonstrated to facilitate solutions that address specific problems in the United States highway bridge infrastructure. Initial material development research on UHPC began more than two decades ago. First structural deployments began in the late 1990s. First field deployments in the U.S. highway transportation infrastructure began in 2006. For this study, UHPC-class materials are defined as cementitious-based composite materials with discontinuous fiber reinforcement that exhibit compressive strength above 21.7 ksi (150 MPa), pre- and post-cracking tensile strength above 0.72 ksi (5 MPa), and enhanced durability via a discontinuous pore structure. This report documents the state of the art with regard to the research, development, and deployment of UHPC components within the U.S. highway transportation infrastructure. More than 600 technical articles and reports covering research and applications using UHPC have been published in English in the last 20 years, with many more published in other languages. The report includes information about materials and production, mechanical properties, structural design and structural testing, durability and durability testing, and actual and potential applications. The report concludes with recommendations for the future direction for UHPC applications in the United States.

https://rosap.ntl.bts.gov/view/dot/26387/dot_26387_DS1.pdf

Ultra-High Performance Concrete: A State-of-the-Art Report for the Bridge Community

Alkali-silica reactions (ASR): literature review on parameters influencing laboratory performance testing

The effect of limestone on the hydration and microstructural development of ultra high performance concrete (UHPC) with different levels of replacement (34%, 54% and 74% by volume) was investigated. Up to 54% replacement of cement by limestone the mixes showed better workability and higher compressive strength (170 MPa at 56 days for 54% addition) compared to a classical mix (155 MPa) with no limestone replacement. The kinetics of hydration were compared for different replacement levels using isothermal calorimetry. The phase development was quantified by X-ray diffraction with Rietveld method combined with thermal gravimetric analysis. The pore structure was examined by mercury intrusion porosimetry. The composition of hydration products was determined by scanning electron microscopy with energy dispersive X-ray analysis. The results showed that the hydration degree of the cement is increased from 39% for classical UHPC to 66% for the UHPC with 54% of limestone.

Effect of cement substitution by limestone on the hydration and microstructural development of ultra-high performance concrete (UHPC)

Sulfate attack on cementitious materials containing limestone filler — A review

Effect of ettringite on thaumasite formation

Effect of TEA on Fly Ash Solubility and Early Age Strength of Mortar

Effect of Heat Treatment Method on the Properties of UHPC

Enhanced damage due to the alkali–silica reaction (ASR) in concrete exposed to deicing salt (NaCl) is usually attributed to binding of chloride ions in the hydration products of cement. To balance charge, OH− ions are released into the concrete pore solution which increases alkalinity. However, during NaCl ingress a decrease in the OH− concentration of the concrete pore solution due to potassium leaching would reduce SiO2 solubility and therefore ASR damage. The present work combines expansion measurements with pore solution analysis by ICP-OES and XRD measurements on concretes and hydrated cement pastes. Solubility equilibria calculations were performed with the hydrogeochemical simulation program PHREEQC. The investigations show that the OH− concentration of the pore solution is mainly lowered by potassium leaching during NaCl ingress. The OH− concentration also decreases owing to the formation of Friedel’s salt from ettringite which is associated with the release of sulphate. Although the OH− concentration with NaCl is lower, ASR damage is intensified and the silicon concentration in the pore solution is higher. Higher silicon solubility is explained by the higher total alkali concentration which increases surface silicate solubility, the formation of an aqueous complex NaHSiO
 3
 0
 and a higher ionic strength. These effects promote the sensitivity of silicate minerals to ASR, the formation of alkali silica gel and finally ASR damage.

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Ingress of NaCl in concrete with alkali reactive aggregate: effect on silicon solubility

In this paper, the favorable chemical composition of alternative hydraulic cementitious binder (HCB) consisting of synthetic α-C2S hydrate and quartz, as well as the impact of tribochemical—thermal treatment on HCB properties was determined. Hydraulic cementitious binder was prepared by mixing synthetic α-C2S hydrate and quartz sand (the ratio was equal to 1:1 by mass), homogenizing in a homogenizer at 34 rpm for 30 min. Tribochemical activation was carried out in vibratory disk mill at 950 rpm for 2, 5, 10, and 20 min. It was estimated that the tribochemical activation affects the properties of HCB because a higher fineness provides a greater surface area to be wetted, and also results in an acceleration of the reaction between HCB and water. It was determined that the favorable tribochemical activation time for α-C2S hydrate is 5 min. Meanwhile, the investigation of the influence of quartz quantity in composition showed that at least 50 % of it is essential. Also, these studies showed that coupled application of tribochemical and thermal activation helps to create HCB samples with higher reactivity. In addition, it was determined that the best conditions are when α-C2S hydrate and quartz sand ratio is 1:1, tribochemical activation time in vibratory disk mill at 950 rpm: 5 min, thermal activation temperature: 450 °C, duration: 30 min. HCB made under these conditions has 3.7 m Wg−1 of heat flow and is similar to Portland cement.

Liudvikas Urbonas

Papers

Effect of ettringite on thaumasite formation

Effect of TEA on Fly Ash Solubility and Early Age Strength of Mortar

Effect of Heat Treatment Method on the Properties of UHPC

Ingress of NaCl in concrete with alkali reactive aggregate: effect on silicon solubility

Tribochemical and thermal activation of α-c2s hydrate as precursor for cementitious binders