Investigation of the influence of blast-furnace slag on the resistance of concrete against organic acid or sulphate attack by means of accelerated degradation tests

To tackle the rising CO2 concentration in atmosphere, technologies of carbon sequestration are emerging. As one of these technologies, carbonation curing of cement-based composite at early age shows a great potential because its wide application and benefits to provide cement-based composite with enhanced mechanical properties and durability. However, carbonation curing is mostly investigated on lab-scale, due to two main challenges that should be addressed before it can be widely applied for industrial-scale production: (1) CO2 sequestration rate is still low, which is around 20 %–50 % of the theoretical potential because of the limitation of CO2 diffusion into matrix during the carbonation curing; and (2) the effect carbonation curing on the durability of cement-based composites and the underlying mechanisms remains unclear, especially for some critical aspects such as alkali-silica reaction, corrosion, and sulfate attack. Therefore, this paper focuses on discussing: (1) factors affecting CO2 sequestration in cement-based composite during each stage of carbonation curing and the optimization methods of carbonation curing for high CO2 sequestration rate without mitigating mechanical properties and durability, and (2) effects of carbonation curing on different aspects of durability and the corresponding mechanisms. Based on the review, future studies on addressing current challenges are inspired to comprehend and promote the carbon sequestration by carbonation curing of cement-based composites.

Fundamental understanding of carbonation curing and durability of carbonation-cured cement-based composites: A review

Study of deterioration of concrete exposed to different types of sulfate solutions under drying-wetting cycles

Effect of interfacial transition zone on the transport of sulfate ions in concrete

Deformation behaviour of concrete materials under the sulfate attack

Micro-analysis of the role of interfacial transition zone in “salt weathering” on concrete

Normally, concrete technologists attribute salt weathering, salt crystallization or physical attack to the deterioration of concrete that is partially exposed to sulfate environment. However, there are few convincing evidences supporting this view. The purpose of this paper is to check by means of extensive micro-analysis if traces of sulfate crystals are present in the paste. This would enable to verify in a direct way whether salt weathering really causes cement paste damage or not. In this research, cement paste and cement–fly ash paste specimens were partially exposed to sodium sulfate and magnesium sulfates solution under a constant storage condition (20 ± 2 °C, and 60 ± 5% RH) and a sharply fluctuating environment (40 ± 2 °C and 35 ± 5% RH for 24 h, then 10 ± 1 °C and 85 ± 5% RH, also for 24 h) respectively. ESEM and SEM images, combined with EDS and XRD analysis, were employed for micro-analysis. The experimental results indicate that Na2SO4 crystals or MgSO4 crystals could not be identified in the cement paste or the cement–fly ash paste, both under constant and fluctuating exposure conditions. Instead, large amounts of ettringite, gypsum and brucite were found and identified as probably one of the determining factors causing failure of cement paste. On the other hand, salt crystallization could be observed in the calcium carbonate crystals, the carbonated products of hydrated cement paste.

Micro-analysis of “salt weathering” on cement paste

The invention discloses a fastening method of steel-self density concrete composite construction, which is characterized by the following: adopting steel-concrete composite structure; adopting self density concrete on concrete material; proceeding original concrete structure element surface treat; assembling steel; stirring and casting self density concrete; demoulding; curing. This invention possesses simple and stable construction, which can increase bearing capacity, stability and fatigue resistance property of the concrete structure.

Steel-self dense concrete built-up construction reinforcing means

Sulfuric acid attack on concrete has been reported for over a century. Many scientific papers deal with the issue of concrete damage due to sulfate and sulfuric attack. The introduction of self-compacting concrete introduces new questions related to the behaviour of powder-rich mixtures in a sulfate environment.
This paper describes a simple testing method to investigate the influence of the concrete composition on the sulfuric acid attack. Concrete samples have been submerged in a sulfate solution, with a pH varying between 1.7 and 2.0. The mass variation has been recorded during 26 weeks, and the compressive strength of the submerged samples has been compared with reference samples at an age of 6, 13 and 26 weeks. Results indicate that SCC with limestone filler shows a significantly higher resistance against sulphuric acid attack, compared with SCC with fly ash and quartz filler and compared with traditional concrete. The type of superplasticizer does not have a significant influence.

Influence of self-compacting concrete composition on sulfuric acid attack

When concrete elements are partially exposed to sulfate environment, in the upper part of concrete elements above ground an aquiferous zone containing almost saturated and high pH value (> 12.5) sulfate pore solution will be formed. The concentration of sulfate solution is much higher than 5 %, as usually used in laboratory. It is necessary to study the performance of cement-fly ash paste in different high concentration sulfate solutions at different temperatures.
In this paper, pure cement paste and cement - fly ash (25 % dosage) paste specimens were immersed in the 5 %, 15 %, 20 %, 30 %, 40 % and 50 % sodium solutions at 20°C, 30°C and 40°C respectively. After 1, 3 and 6 months immersion, the compressive strength of the specimens was measured. XRD and thermal analysis were employed to analyze the reactive products of the paste. The experimental results show that the reactive aluminum in fly ash is activated by high concentration sodium sulfate solution at different temperatures and more ettringite is generated than pure cement paste.

https://biblio.ugent.be/publication/1266102/file/1266136.pdf

Zanqun Liu

Papers

Micro-analysis of the role of interfacial transition zone in “salt weathering” on concrete

Micro-analysis of “salt weathering” on cement paste

Steel-self dense concrete built-up construction reinforcing means

Influence of self-compacting concrete composition on sulfuric acid attack

Study of cement-fly ash paste exposed to sodium sulfate solutions with different concentrations at different temperatures