Deterioration Process of Cementitious Material Properties under Internal Sulphate Attack

Internal sulfate attack in mortars containing contaminated fine recycled concrete aggregates

Combined effect of alkali-aggregate reaction (AAR) and internal sulfate attack (ISA): Microstructural and porous structure modifications of portland cement mortars

Effect of crystalline admixture and polypropylene microfiber on the internal sulfate attack in Portland cement composites due to pyrite oxidation

Research Sulfate Resistance of Cement-Containing Composition

Sand contaminated with sulphates is a local problem in the Middle East Area. It is difficult to obtain well graded sand with sulphate content within the limits specified by international standards. International standard adopt different concepts in limiting internal SO3 contents in concrete. Some standards put maximum limits for SO3 by weight of aggregate only, other standards, limit the total SO3 in concrete by weight of cement in the concrete, while surprisingly a third group has no limitation on internal SO3 in concrete. In this research work, an attempt was made to study the possibility of adopting the second concept only (total SO3 in concrete by weight of cement) and overlook all other concepts, as it reasonably provides a complete picture of the presence of sulphates in the concrete mix. This work focuses only on internal sulphate attack, and investigates different concrete mixes with compressive strengths between 15 and 75 MPa. In these mixes sand with SO3 between 0.5% and 2.0% was used, thus yielding total SO3 contents by weight of cement in the range of 3.2–10.5%. Two important properties concerning sulphate attack were studied; these were; compressive strength and expansion in water up to 180 days. From the results obtained, it was found that increasing the concrete compressive strength, resulted in increasing its resistance to internal sulphate attack, and concrete mixes with high strength (>45 MPa) had almost the same expansion in water, despite the increase in the sulphate content in the sand from 0.5% to 2.0%. As a result of this work, it was clear that it is better to specify total sulphates in concrete as a percent by weight of cement, rather than limiting sulphates in aggregates as specified in some international standards. Based on the present results, it was concluded that new values of total SO3 content in concrete by weight of cement can be specified at 6.0%, 5.5% and 5.0% for concrete mixes with cement contents <400, 400–500 and above 500 kg/m3 respectively regardless to SO3 contents in the aggregates.

The relationships between concrete curing procedures, materials composition, and internal sulfate attack damage will be discussed in view of the experience obtained in Europe in the 1970s and 1980s. The heat-treatment procedures that were introduced and specified to eliminate or minimize the damage will be highlighted and suggestions will be made as to the needed adjustments in curing practices.

Sulfate attack of cement matrix containing inorganic alkali-free accelerator

Municipal solid waste incinerator bottom ash was evaluated for its alkali aggregate reactivity in cement mortars. Subsequently, two wastes were evaluated as supplementary cementitious materials for their efficacy in mitigating expansive alkali-silica reactions in cement mortars amended with bottom ash. Three bottom ashes were incorporated into mortar bars as 15, 30 and 50% replacements of non-reactive sand. Control MSWI amended mortars were compared to those containing coal fly ash and glass pozzolan (synthetic glass). Dimensional expansion of the mortars was measured over 14 days to quantify the extent to which the recycled coal fly ash and glass pozzolan mitigated the alkali reactivity of the ash-amended mortar specimens. Average expansions of the ash-amended mortars ranged from 0.10 to 0.40%, suggesting that ash components reacted expansively in an alkaline environment. Microscopic analysis was used to complement the data and confirm the presence of silica-rich gel within glass fragments of the ash, as well as cracking of the aggregates. Supplementary cementitious materials (class F coal fly ash, glass pozzolan) mitigated expansion of the mortars by 90% on average, likely through consumption of the alkalis in the paste pore water.

To investigate the durability of cementitious materials under complex environmental conditions in Xinjiang, this study conducted durability tests on mortar specimens with different fly ash contents under dry/wet sulfate attack conditions, with standard curing and steam curing at 70 °C. The appearance loss and flexural and compressive strength variations in the specimens were analyzed, and an evolution model of the mortar strength under a dry/wet sulfate attack was established. Moreover, XRD and SEM techniques were used to characterize the erosion products and microstructure, and to explore the erosion resistance mechanism of fly ash cementitious materials. The results showed that, after 160 cycles of erosion, the flexural strength of the specimens decreased with the increase in the fly ash content. In the context of steam-cured mortar specimens, throughout the entire erosion period, specimens with a fly ash content of 45% exhibited the highest relative compressive strength. The established strength evolution model had a minimum determination coefficient of 0.879, indicating a good agreement between the model and experimental results. Microscopic research showed that fly ash would undergo a pozzolanic reaction under the action of sulfate and calcium hydroxide, which was beneficial to the improvement of the erosion resistance. As the fly ash content increased, the erosion products of the specimens gradually became dominated by gypsum.

In County Donegal, northwest Ireland, thousands of homes built with concrete blocks show an increasing degree of severe structural defects attributed to high mica content in the aggregates. Consequently, the problem is popularly known as the “Mica Crisis”. In this project the concrete blocks of four affected homes are investigated by microstructural and chemical analysis combined with thermodynamic modelling.Apart from mica, the aggregates contain iron sulphides mainly in the form of pyrrhotite. The sulfur content of the aggregates considerably exceeds the limit value defined by the European standard for concrete aggregates (EN 12620). The results of the microstructural analysis coupled with thermodynamic modelling demonstrate that the concrete suffers from internal sulfate attack triggered by pyrrhotite oxidation. The comparison of the results of this investigation with the data collected by chartered engineers on almost hundred damaged homes shows that the four investigated cases are representative of the situation in Donegal.

To investigate the influence of sulfate erosion on the performance of cement-based materials, this study designed cement paste, mortar and concrete specimens with a water-to-cement ratio of 0.35. The study examined the changes in performance over 30 days, 60 days, 90 days, 120 days, and 150 days of sulfate erosion, and the findings showed that: as the duration of sulfate erosion increased, the mass change and compressive strength of cement-based materials generally showed an increasing trend first and then decreasing trend. The mass change of cement paste, mortar and concrete specimens was 0.64%, 0.274%, and 0.16%, respectively, after 150 days of sulfate erosion. The compressive strength of the 150-day cement paste, mortar, and concrete decreased by 56.86%, 14.29%, and 19.34% respectively.The porosity of cement paste, mortar and concrete specimens showed that the porosity of cement paste was greater than that of concrete, which was greater than that of mortar specimens.When employing the Mercury Intrusion Porosimetry (MIP) test, the porosity of mortar specimens decreased initially and then increased with prolonged sulfate exposure. The porosity of mortar specimens reached 12.57% after 30 days of sulfate erosion and 18.27% after 150 days of sulfate erosion.When Nuclear Magnetic Resonance (NMR) testing was adopted, the variation law of porosity after sulfate attack was basically consistent with that of MIP testing, but there were differences in porosity. The porosity was 7.60% after 30 days of erosion and 14.42% after 150 days of erosion. A comprehensive comparison of the two testing methods revealed numerical differences, but it could provide a more comprehensive understanding of the influence mechanism of pore structure on the performance of cement-based materials, and offer important references for optimizing material ratios and improving material performance.Supplementary InformationThe online version contains supplementary material available at 10.1038/s41598-025-31233-5.

Deterioration of mortars exposed to sulfate attack under electrical field

Characterization of a mortar made with cement and sludge from the light-emitting diode manufacturing process

Degradation mechanism of blended cement pastes in sulfate-bearing environments under applied electric fields: Sulfate attack vs. decalcification

Sulfate attack is a major threat to the durability of concrete structures and causes surface scaling, expansive disruption, and loss of cohesion of cement hydration products. Properties such as expansion strain or the mass loss ratio of the concrete specimens are commonly used in lab testing to identify the deterioration of concrete under sulfate attack. However, these indicators and testing methods are rarely used for the in situ monitoring of concrete structures in aggressive sulfate environments since sulfate attack typically occurs either underground or below the water level. In this study, an active sensing method is proposed to monitor the deterioration of concrete exposed to a sulfate attack. Three concrete specimens with embedded smart aggregates were fabricated to measure the wave velocity at different concrete depth ranges and sulfate attack times, and 48 cubic specimens were cast to measure the compressive strength development of concrete in water or an 8% sulfate sodium solution. The test results showed that the measured wave velocity was sensitive to the deterioration level of concrete. This indicates that the sulfate attack level can be evaluated with respect to the concrete depth using the proposed monitoring method. A preliminary relationship between the measured wave velocity and deteriorated strength of concrete specimen was established. This study provides a valuable insight into the use of in situ health monitoring and a useful strength prediction method for concrete structures experiencing a sulfate attack.