Curing Practices and Internal Sulfate Attack—The European Experience

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

Internal sulfate attack in mortars containing contaminated fine recycled concrete aggregates

As one of the important factors affecting the structural durability of cementitious materials, sulphate erosion not only reduces the service life of the material but also poses a threat to the structural safety of the project. At present, scholars around the world have conducted extensive research on topics related to external sulphate attacks and have achieved fruitful results. However, the process and mechanism of attack degradation of the gelling material are not clear. In this paper, gypsum sand was introduced into the mortar. The effects of gypsum content, gypsum particle size and curing temperature on physical properties such as expansion and strength of specimens were investigated. X-ray diffraction (XRD), thermogravimetry (TG), differential scanning calorimetry (DSC), Scanning Electron Microscopy (SEM) and energy dispersive spectrometry (EDS) were used to analyse specimens’ phase composition and microstructure evolution at different attack ages. Finally, cementitious materials’ degradation process and mechanism under internal sulphate attack (ISA) were analysed. Through the above research, the following main conclusions are drawn: (1) The swelling rate of cement mortar specimens all increased with the increase of gypsum dosing; (2) The expansion of cement pastes and mortars does not increase with the increase in curing temperature; (3) The gypsum particle sizes are smaller, the expansion of mortar specimens is larger, and the loss of compressive and bending strength of mortar specimens is large; and (4) The main reaction product of ISA is Ettringite (AFt). The gypsum formed during the ISA process does not cause expansion, while AFt is the main reason for the destruction of the cementitious material.

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.

Research Sulfate Resistance of Cement-Containing Composition

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.

Cracking of residential concrete foundations in eastern Connecticut, USA from oxidation of pyrrhotite

Deterioration of residential concrete foundations: The role of pyrrhotite-bearing aggregate

This study investigated the degradation behavior of cast-in-situ mortar incorporating iron ore tailings (IOTs) as a partial replacement for river sand under combined attack involving sulfate, magnesium, and chloride ions (distilled water, internal attack, external attack, and internal–external attack). Throughout the exposure period, changes in appearance, size, mass, and mechanical properties were monitored; meanwhile, microstructural, mineralogical, and pore structure evolution were characterized using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD), thermogravimetry/differential thermogravimetry (TG/DTG), and nuclear magnetic resonance (NMR). The results indicate that the incorporation of 25% IOTs demonstrates optimal mechanical properties and attack resistance. Internal attack more significantly impairs the mechanical improvement from 25% IOTs. The compressive strength increases by 17.65% under external attack alone, in contrast to less than 10% for internal or combined attack. At 50% IOTs content, the improvement effect is significantly reduced compared to that at the 25% content.

One of the most aggressive attacks to which cement-based materials can be exposed is that produced by sulphate. During this attack, expansive products are formed, causing volumetric strains in hardened materials, which brings microcracking and the reduction of their strength and durability. The use of non-destructive techniques for characterizing the microstructure of cement-based materials, and for following the development of deleterious processes which can affect them, has become an important research field. Among them, non-linear ultrasonic (NLU) techniques have shown to be useful for evaluating the material degradation. The aim of this work is to study the possibility of using the NLU technique for the non-destructive evaluation of initial development of internal sulphate attack in cement-based materials. Cement pastes were prepared using ordinary Portland cement, to which an appropriate amount of calcium sulphate 2-hydrate was added during the setting for producing an internal attack in the samples. Furthermore, its effects in the microstructure have been followed with mercury intrusion porosimetry. The expansion and linear ultrasonic pulse velocity were also determined. The preliminary results indicate that the NLU technique could be useful for studying the development of sulphate attacks in the short-term, complementing the information provided by other techniques.

As usually the composition/formation for concrete mixing there has 1 part of cement : 2 parts of sand : 3 parts of crushing stone (1:2:3) or 1 part of cement : 1,5 parts of sand : 2,5 parts of crushing stone (1:1,5:2,5) to be reckoned and also usually doing in Banyumas Regency. In spite of this case to make problems: (i) if the composition/formation for concrete mixing as above has usually already exactly use for base material/raw material condition like sand and crushing stone to be in stock in several places round about Banyumas Regency; (ii) when is’nt it, therefore how much the composition/formation for concrete mixing exactly good based to the base material/raw material condition to be in stock in several places round about Banyumas Regency; and (iii) when the composition/formation for concrete mixing is exactly/good to be able to known and after that how many strong of the characteristic compression can be reach by several composition/formation for concrete mixing use the material to be come from several places round about Banyumas Regency as above mentioned. The problems as above mentioned to be important to examined because with the condition of base material/raw material to be in stock suppose that the concrete mixing composition not as usually, this case must be important to prove because Banyumas Region and round about it has many base material/raw material but not yet efficiency use with the exactly composition. From the result of examination which to execute in laboratory based on sive analysis and concrete cube test (crushing test) determined the concrete mixing composition for the materials to be in stock from several places round about Banyumas Regency, there was 1 part of cement : 2 parts of sand : 2 parts of crushing stone (1:2:2) not as usually and the concrete characteristic compression (s bk ) was about between 181,50 kg/cm 2 – 242,53 kg/cm 2 . Keywords: Concrete Composition, Concrete Characteristic Compression Permalink: http://www.ejournal.undip.ac.id/index.php/mkts/article/view/3890 [How to cite: Gandadinata, I., 2004, Komposisi dan Kekuatan Tekan Beton Karakteristik pada Campuran Semen Nusantara, Pasir dan Split dari Beberapa Tempat di Sekitar Kabupaten Banyumas, Jurnal Media Komunikasi Teknik Sipil , Volume 12, Nomor 3, pp. 84-90]

A thermomagnetic technique to quantify the risk of internal sulfur attack due to pyrrhotite

This work is concerned with the study of the effect of cement types, particularly OPC and SRPC, which are the main cement types manufactured in Iraq. In addition, study the effect of mineral admixtures, which are HRM and SF on the resistance of high performance concrete (HPC) to internal sulphate attack. The HRM is used at (10%) and SF is used at (8 and 10)% as a partial replacement by weight of cement for both types. The percentages of sulphate investigated are (1,2 and 3)% by adding natural gypsum as a partial replacement by weight of fine aggregate. The tests carried out in this work are: compressive strength, flexural strength, ultrasonic pulse velocity, and density at the age of 7, 28, 90 and 120 days.&#x0D; The results indicated that the SRPC mixes showed lower reduction in the properties of concrete compared to OPC mixes at all ages of test. The greatest reduction in compressive strength was at the age of (90) days for OPC mixes and the age of (28) days for SRPC mixes. After that, the concrete showed the lower reduction for all percentages of sulphate in fine aggregate. The results also indicated that the performance of HRM showed better results than the SF, and the replacement of 10% SF exhibits better results than 8% SF for both types of cement.&#x0D; &#x0D;

Contamination of aggregates with sulfate salts (especially gypsum) is a major problem in Middle East concrete construction. Fine aggregate has more detrimental effect due to its large surface area (fineness). An experimental work had carried out to investigate the behavior of high performance concrete exposed to internal sulfate attack in comparison with traditional concrete. Four sulfate contents (0.5, 1.5, 2.0, and 2.5 %) in fine aggregate were studied. Metakaolin was used as a pozzolanic material, which has proved itself as a good active one. Teasing program included compression, splitting, and ultrasonic pulse velocity tests. 168 cubes and 216 cylinders were cast throughout this program. The test period was extended to 210 days. The harmful effect (reduction in strength) of sulfate was obvious in early ages in contrast to external attack (as early as 7 days). The reduction in strength was continuous and higher in later ages and for higher SO 3 contents with reference to the mix with 0.5% SO 3 . Test results showed that high performance concrete had lost strength, in such an environment, but it was more resistant than normal concrete and it may gain strength with age due to the pozzolanic action of metakaolin. The ultrasonic velocity results were positively proportional to strength development but with a slower rate of variation.