Resistance of self-consolidating concrete to ammonium sulphate attack

With the growing use of self-consolidating concrete (SCC) in various infrastructure applications, it has become necessary to establish reliable data on its long-term durability since its mixture design, rheology and consolidation are different than that of normal concrete. Several applications of SCC involve its exposure to chemical attack, particularly to sulphate-rich media such as wastewater treatment facilities, industrial and agricultural zones which also encompass ammonium cations. Thereby, this study aims at investigating the resistance of a wide scope of SCC mixture designs to ammonium sulphate attack. Specimens from 23 SCC mixtures were continuously immersed in a high concentration ammonium sulphate solution with controlled pH (6.0?C8.0) up to 54?weeks. The main test variables included the type of binder (single, binary, ternary and quaternary), air-entrainment, sand-to-total aggregates mass ratio, and the inclusion of fibre reinforcement (single and hybrid). The SCC specimens showed variable degrees of deterioration after 54?weeks, indicating different modes of degradation. The study highlights the role of ternary and quaternary binders in improving the resistance of SCC to ammonium sulphate attack. It is also emphasized that multiple performance indicators are needed to achieve a reliable assessment of cement-based materials under ammonium sulphate attack.     

Thaumasite sulphate attack at the concrete structures of the Ferenc Puskás stadium in Budapest

After World War II, in order to minimise the significant cement deficiency (caused by the demand of restoration works and prestigious capital investments of the governing regime) a clinker saving cement mix named ‘Sigma Cement’ was produced in Hungary. The patent lay in replacing the coarse clinker particles with limestone powder. Under the effect of waste gases from the nearby railway station and rubber plant the structural concrete of the largest Hungarian Sports Stadium suffered significant damages due to carbonisation and sulphating in which thaumasite sulphate attack may have played its role.     

Resistance of concrete and mortar against combined attack of chloride and sodium sulphate

Marine environments are typically aggressive to concrete structures, since sea water contains high concentrations of chlorides and sulphates. To improve predictions of concrete durability within such environments, it is important to understand the attack mechanisms of these ions in combination.In this research, the reciprocal influence of Cl⁻ and SO₄²⁻ was investigated for four mixtures, namely with Ordinary Portland Cement, High Sulphate Resistant cement, and with Blast-Furnace Slag (50% and 70% cement replacement). Chloride penetration depths and diffusion coefficients were measured to investigate the influence of SO₄²⁻ on Cl⁻ attack. Besides, length and mass change measurements were performed to examine the influence of Cl⁻ on SO₄²⁻ attack. Since the formation of ettringite, gypsum and Friedel’s salt plays an important role, XRD-analyses were done additionally.It can be concluded that chloride penetration increases when the sulphate content increases at short immersion periods, except for HSR concrete. Concerning the sulphate attack, the presence of chlorides has a mitigating effect.     

Durability of self-consolidating concrete to combined effects of sulphate attack and frost action

The worldwide shift towards performance-based standards for concrete demands the advent of performance tests that combine more than one damage mechanism. Such tests can be more reliable in evaluating emerging concrete types such as self-consolidating concrete (SCC). Several applications of SCC involve its exposure to both freezing–thawing cycles and chemical attack, particularly to sulphate-rich media. This study aims at investigating the durability of SCC to sulphate attack coupled with frost action. Potential performance risks of SCC under this dual exposure were identified in terms of various mixture design parameters. Deterioration in physico-mechanical parameters was related to thermal, mineralogical and microscopy analyses, which demonstrated the complex mutual effects of sulphate attack and frost action on SCC specimens. It is shown that SCC mixtures that perform well under the classical ASTM C 1012 test can fail under coupled exposure to freezing–thawing cycles and sulphate attack.     

Analysis of prestressed concrete slab-and-beam structures

 In this paper a solution to the problem of prestressed concrete slab-and-beam structures including creep and shrinkage effect is presented. The adopted model takes into account the resulting inplane forces and deformations of the plate as well as the axial forces and deformations of the beam, due to combined response of the system. The analysis consists in isolating the beams from the plate by sections parallel to the lower outer surface of the plate. The forces at the interface, which produce lateral deflection and inplane deformation to the plate and lateral deflection and axial deformation to the beam, are established using continuity conditions at the interface. The influence of creep and shrinkage effect relative with the time of the casting and the time of the loading of the plate and the beams is taken into account. The estimation of the prestressing axial force of the beams is accomplished iteratively. Both instant (e.g. friction, slip of anchorage) and time dependent losses are encountered. The solution of the arising plate and beam problems, which are nonlinearly coupled, is achieved using the analog equation method (AEM). The adopted model, compared with those ignoring the inplane forces and deformations, describes better the actual response of the plate–beams system and permits the evaluation of the shear forces at the interfaces, the knowledge of which is very important in the design of prefabricated ribbed plates. Received 1 June 2000     

Procedures for assessing thaumasite sulfate attack and adjacent ground conditions at buried concrete structures

In 1998 Halcrow were appointed by the Highways Agency to investigate the thaumasite form of sulfate attack at the buried concrete foundations of structures on major highways in Gloucestershire, UK. Detailed investigations were completed at 28 structures and the results used to apply a risk assessment procedure to a further ninety structures. Standard procedures for sampling, testing and classifying soil, groundwater and concrete were devised to ensure that rigorous statistical analyses of the data could be applied. The procedures were also designed to meet the then current UK guidance notes, BRE. Digest 363 [Building Research Establishment, Sulphate and acid resistance of concrete in the ground, BRE Digest 363, CRC Press, Boca Raton, 1996] and the Thaumasite Expert Group Report [Thaumasite Expert Group, The thaumasite form of sulfate attack: Risks, diagnosis, remedial works and guidance on new construction, DETR, 1999] and are compatible with the subsequent BRE Special Digest 1 [Building Research Establishment. Concrete in aggressive ground, Part 1: assessing the aggressive chemical environment, BRE Special Digest 1, CRC, Boca Raton, 2001]. Recommendations are made for applying many of the procedures that have been developed to future site investigations to enable consistency, compatibility and easier data transfer for future research on the thaumasite form of sulfate attack.     

Analysis of shrinkage deformations in concrete structures

An analytical method for predicting shrinkage deformations in both cracked and uncracked states is discussed. The validity of this method was verified by conducting an experimental investigation in which deformations due to shrinkage were measured for more than 300 days in the laboratory. The curvatures due to shrinkage were found to be different in cracked and uncracked states. The introduction of compression reinforcement was found to reduce the shrinkage curvatures, whereas increase in tension reinforcement was found to increase shrinkage curvatures. Equations presented here for computing these deformations compare fairly well with experimental data and are recommended to be used in the serviceability analysis of concrete members.     

New procedure to investigate external sulphate attack on cementitious materials

In order to predict the durability of concrete structures in contact with sulphate rich environments, laboratory tests have to be sufficiently representative of the field conditions. This study is focused on the degradation of cement-based materials submitted to external sulphate attack. To be close to the natural degradation process, a new experimental procedure has been developed on the basis of two studies. The first was conducted on concrete and showed the deficiencies of common experimental programs only based on the measurement of the expansion. The second investigated the relation between the specimen size and the resistance to sulphate attack. As a result, the basic points of a representative procedure were identified. The mass and length of the specimens were monitored. The pH of the sodium sulphate solution was controlled, which allowed the assessment of leaching kinetics.This procedure was then validated by analysing, at macroscopic and microscopic scales, the influence of the water sulphate concentration on the behaviour of cementitious materials. The accelerating effect of high sulphate concentrations is due to the increase in leaching kinetics rather than the type of expansive products. Whatever the concentration, the same critical proportion of the cross section is required to generate global swelling.     

Thaumasite attack on concrete at Marbjerg Waterworks

Marbjerg Waterworks, run by ‘Copenhagen Energy’ and a supplier of drinking water for Copenhagen, was constructed 1932–1934. An inspection of the underside of the water oxidation stairs, only accessible when the waterworks is emptied of water, took place in 1997. The temperature at this part of the waterworks where the ground water enters the plant is 5–8 °C, all year round.

The concrete above the waterline, in the dome-shaped room below the oxidation stairs, showed an attack of an impressive character. The surface layer up to 10–12 mm depth was loose and easy to peel off, in some places like festoons. Further, the columns supporting the oxidation stairs showed an attack at and above the water table similar to a sulfate attack typical for the Middle East region.

Concrete samples were examined by thin section microscopy, identifying sulfuric acid and thaumasite as the causes of the spalling. Bacterial conversion of hydrogen sulfide to sulfuric acid was part of the proposed reaction mechanisms.

Attack on the concrete was noted only from the underside of the stairs, and above the water table, but no attack was seen on top of the oxidation stairs or other concrete parts permanently exposed to running water. Awareness is recommended to such hidden concrete attack under similar conditions.     

A state-of-the-art review on delayed ettringite attack on concrete

The paper presents a critical review of the sulphate attack related to ettringite formation. This process is associated with expansion. However, not necessarily any ettringite-related expansion is related to the sulphate attack. For example, early ettringite formation which occurs immediately (within hours) in a plastic fresh mixture does not produce any damaging expansion and is associated with the regulation of setting time of Portland cement paste. Expansion after the hardening of cement paste can be advantageously used for the development of chemical prestress in expansive cements. Delayed ettringite formation (DEF) occurs at late ages and the related heterogeneous expansion in a hardened concrete can produce cracking and spalling. Two different types of DEF are examined depending on the sulphate source: DEF caused by external sulphate attack or internal sulphate attack.     

Behaviour of foam concrete under sulphate environments

This paper reports the effects of variation in density, concentration and type of cation associated with sulphate on the expansion, mass and strength loss of foam concrete produced with two synthetic surfactants. Comparisons are made between behaviour of foam concrete of different densities and that of corresponding base mixes of mortar without foam. The investigations indicated that the expansion in sodium sulphate environment was up to 28% higher than that of magnesium sulphate environment which can be attributed to greater quantum of ettringite formation in sodium sulphate environment. The major deterioration mechanism in magnesium sulphate environment is disintegration of cementing material and this contributed to loss in mass of 1% and higher sulphate deterioration factor of 0.4 for specimens under very severe magnesium sulphate environment. Irrespective of the type of sulphate environment, the deterioration of foam concrete was lower than that of base mix.     

Identification of acid attack on concrete of a sewage system

A sewage system, 300 km long, showed superficial deterioration of concrete just 2 years after construction. In order to re-habilitate the structure, it was necessary to identify the main mechanism of deterioration and to understand the heterogeneous distribution of the damage observed. The study was performed in a three stepped program: site investigation and sampling, laboratory tests and concrete petrography. During the site inspection it was recognized that there was dissolution of the concrete in some sectors of the structure, with the aggregate particles protruding in relation to the undulated surface. In some places a white to yellowish putty-like product could be excavated by hand. The main deterioration was observed above the water level. The composition of the atmosphere inside the sewer was assessed and a high content of hydrogen sulfide was detected. Sampling was performed in different structural elements which showed diverse exposition to the aggressive environment. Impregnated thin sections of concrete with fluorescent yellow dye were analyzed by optical microscope. Concrete petrography showed to be crucial for the diagnoses. The study showed that the putty-like product was composed by gypsum with small residual particles of siliceous sand which resisted to the acid attack. SEM/EDS was used to evaluate the content of sulfur in different sections of the concrete cores and also to characterize the putty-like product at the surface of the concrete. This study led to the confirmation of the presence of an extensive sulfuric acid attack with rather minor sulfate attack within the concrete due to the exposition to aggressive environment. It also showed that behind the superficial deteriorated level, the concrete was sound with no signs of internal deleterious reactions. Ammonium content in residual water might have also contributed to the superficial deterioration of the concrete sewer.     

Rehabilitation of concrete structures

Report of an International Conference held by RILEM and organized by the CSIRO Division of Building. Construction and Engineering, Melbourne, and the Australian Concrete Repairs Association, Melbourne, in cooperation with RILEM Technical Committee TC 124 ‘Repair Strategies for Concrete Structures Damaged by Steel Corrosion’.     

Research and following of concrete structures

The importance and interest of applied research for improving knowledge on the long-term structural behaviour of concrete structures is increasingly being recognized as a growing number of relatively recent concrete structures have been found to present pathologic problems that endanger their safety, serviceability and durability.     

Classification of concrete damage caused by chemical attack

The more common chemical reactions involved in the deterioration of concrete are reviewed. Physical manifestations are discussed and illustrated     

Chloride attack of reinforced concrete: an overview

The mechanism of chloride-induced corrosion of steel embedded in concrete, the ingress of chlorides into the concrete, and the threshold chloride content for corrosion to occur are discussed. The binding of chloride ions by cement compounds and the associated effect of using different cements, both Portland and blended, as well as other factors influencing corrosion, are considered. Tests for the penetrability of concrete to chlorides are described. Finally, the prevention of corrosion is discussed.     

The influence of corrosion on bond properties between concrete and reinforcement in concrete structures

The rebar corrosion in reinforced concrete is one of the most extensive pathologies affecting the performance of concrete structures. Chloride-induced rebar corrosion damage results mainly from the use of de-icing salts in cold climates and/or exposure to marine environments. Carbonation damage is a further important degradation mechanism. The internal consequences of corrosion are the modification of the steel behavior and degradation of the steel–concrete bond. This work is devoted to the influence of the controlled corrosion on the adherence between steel and concrete. A new geometry of specimen has been designed to: (i) avoid the lateral confining stresses that appear during the classical pullout tests and (ii) permit to impose a known confinement for the study of its influence on the behavior of the interface. Five specimens with different levels of corrosion have been tested in this contribution. Reinforcing bars embedded in concrete were submitted to accelerated corrosion using an external current source. The magnitude of corrosion was measured using both Faraday’s law and the weight loss method. The level of corrosion varied from 0% to 0.76%. The geometry of the specimens allowed us to take series of digital pictures during the tests, which were analyzed using a digital image correlation, the procedure named CORRELI^LMT. The results of pullout tests proposed in this contribution indicate that: (i) levels of corrosion that are less than 0.4% of weight loss improves the bond stress and (ii) levels of corrosion resulting in more than 0.4% of weight loss lead to a reduction of the bond stress value.