Performance of concrete incorporating GGBS in aggressive wastewater environments

Abstract

Concrete is traditionally used as the main component of wastewater facilities. The sulfate and acidic environment presents significant challenges. Supplementary cementitious materials (SCM) such as GGBS are being used in increasing quantities in concrete and have been shown to provide concrete with increased durability in this particular environment. They have traditionally been used with CEM I, but in recent years a shift in concrete practice has led to the introduction of CEM II cements with reduced CO 2 footprint and obvious environmental and economic benefits. However, the change in cement chemistry associated with using CEM II and GGBS must also be accounted for in concrete specifications for aggressive environments. This has particular importance when concrete is exposed to elevated sulfate and sulfuric acid environments, such as that associated with water and wastewater treatment.The performance of CEM II/A-L cements with varying amounts of GGBS was evaluated through a series of tests conducted to determine their durability characteristics in respect of sulfate attack and sulfuric acid attack. As a benchmark, samples were also tested using CEM I cement, CEM I with GGBS, and a sulfate resistant Portland cement. Results have shown that for all cases, the addition of GGBS resulted in considerable reductions in sulfate induced expansion relative to samples using CEM I or CEM II binders alone. A slight improvement in performance relative to sulphate resisting Portland cement (SRPC) binders was also observed. However in respect of the sulfuric acid environment the regime proved too harsh and ultimately resulted in the early failure of all samples. Some difference in performance was noted, but this was not considered noteworthy. The influence of pH and acid type was studied. The conclusions were that the concretes tested cannot adequately address the durability threat to all parts of wastewater infrastructure over a significant life span due to the extraordinarily harsh nature of this form of attack.

Feasible use of large volumes of GGBS in 100% recycled glass architectural mortar

“…The could be attributed to the extremely low or even zero calcium hydroxide (CH) content in the cementitious material matrices of these two mixes, because of the large volume of GGBS used [33]. This is consistent with the results of those of O'Connell et al [32] who also showed slight increase in mass with GGBS concrete exposed to a sulphuric acid solution. When no CH is available, decalcification of the cementitious matrix begins through disintegration and softening, rather than expansion and cracking caused by sulphate attack [34].…”

“…The GGBS30 and GGBS45 showed an initial gain in mass (within the 1st week) followed by loss in mass at a steady rate for the remaining duration of the test; such effects had been previously observed by others [32]. It can be seen that at week 8, GGBS30 suffered a higher mass loss than the control mix and the loss of GGBS45 was similar to that of the control mix.…”

Corrosion Effects on the Strength Properties of Steel Fibre Reinforced Concrete Containing Slag and Corrosion Inhibitor

“…This serves as an entry point of corrosion initiation and, hence, the process of corrosion being accelerated in a short period. However, the inclusion of steel is a major application of fibre reinforced concrete and finds potential merits for providing high quality construction without rebar and, hence, any costly treatment method cannot be suitable for surface treatment of steel fibres [3,4]. The process of corrosion in fibre reinforced concrete 2 International Journal of Corrosion is phenomenal due to homogenized steel fibre distribution and, hence, more careful attention has to be provided for designing concrete constituents.…”

Ataque de matrizes cimentícias por sulfato de sódio:adições minerais como agentes mitigadores

“…Normalmente, estas, encontram-se intrinsecamente relacionadas e reforçam-se mutuamente, tornando-se impossível separar a causa e o efeito [2]. No caso desta investigação, a presença de íons sulfato (SO 4 2-) provenientes do meio, na solução dos poros da matriz hidratada, resulta em reação com o hidróxido de cálcio (portlandita), silicato de cálcio hidratado (C-S-H) e o monossulfoaluminato de cál-cio hidratado (AFm), formando gipsita (sulfato de cálcio di -hidratado), etringita secundária (AFt) [3,4] e, também, a taumasita (CaSiO 3 .CaCO 3 .CaSO 4 .15H 2 O). A concentração de íons sulfato na solução aquosa dos poros, a composição do cimento Portland utilizado e a permeabilidade e a absorção capilar de água da matriz hidratada são fatores determinantes do grau de degradação por expansão, fissuração, perda de massa e, consequentemente, perda de resistência à compressão e de integridade do concreto, podendo levar a estrutura ao colapso [5].…”