Alkali-aggregate Reaction Research Articles

Effects of adding sugarcane bagasse ash on the properties and durability of concrete

Ashes from biomass burning, such as from sugarcane bagasse, have great potential as supplementary cementitious materials. The sugarcane bagasse ash (SCBA) possesses high pozzolanicity. However, limited studies have investigated the influence of SCBA on the durability of concrete. A knowledge gap exists regarding the influence of these ashes on the lifetime of reinforced concrete in terms of chloride migration and carbonation. Moreover, additional studies on the effects of SCBA on the alkali–silica reaction (ASR) are essential because this ash generally has a high alkali content. In this study, the effects of adding 5%, 10%, and 15% SCBA on the properties and durability (chloride migration, carbonation, and alkali-aggregate reaction) of concrete were investigated. Furthermore, the SCBA pozzolanicity was evaluated and lifetime estimations in terms of chloride ingress and carbonation were performed. The studied ash demonstrated high pozzolanic activity, which reduced the porosity and water absorption by capillarity and increased the mechanical strength of the concrete. However, because the alkaline reserve was reduced, the concrete with SCBA exhibited a higher carbonation rate (up to 69%) and a shorter lifetime regarding carbonation. Nevertheless, all concrete specimens had a lifetime of more than 50 years in an industrial environment, except for that with 15% SCBA. Adding SCBA also reduced the chloride diffusion coefficients, increasing the lifetime by up to 97.3%. SCBA addition of up to 5% mitigated the ASR owing to the pozzolanic reaction and additional C-S-H formation.

Influence of Type of Alkaline Activator on Durability of Alkali Activated Concrete Using Aggregates Capable to Alkali-Silica Reaction

The paper discloses results of durability studies of alkali activated concretes based on different alkali sources using aggregates capable to alkali-silica reaction (ASR). Active aggregates are representing by perlite, andesite, basalt and sandstone. It is shown that the alkali-reactive aggregates, in degree of their influence on expansion deformations occurring in the slag alkaline concretes may be placed in the following row: perlite< sand< sandstone< basalt< andesite, and a growth of expansion deformations is observed with increase in the active silica content in the aggregate. Also it is set that alkaline components, in degree of their influence on the rate of expansion deformations development in the slag alkaline concretes made with reactive aggregates, may be placed in the following sequence: Na2CO3<Na2O SiO2 < NaOH< Na2O 2SiO2.

Alkali–Silica Reactivity of Sand Used in Sand-Coating Fiber-Reinforced Polymer Bars as Internal Reinforcement for Concrete

Abstract New guidelines require that sand particles used to provide a bond between the FRP reinforcing bars and concrete to be free of any expansion due to alkali–aggregate reactions. The current s...

Bauxite Residue as Supplementary Cementitious Material – Efforts to Reduce the Amount of Soluble Sodium

Abstract This study investigates the feasibility of using bauxite residue (BR) as supplementary cementitious material (SCM) for the cement and concrete industry. It is shown from pastes of BR and calcium hydroxide, that BR is highly pozzolanic in nature. The early hydration of cement pastes with BR is accelerated while long-term strength is reduced probably due to the alkaline nature of BR. To be used as cement replacement material in concrete, attempts have been made to reduce the alkali content of BR, in particular to reduce the chance of alkali-aggregate reactions. Co-calcination of BR with kaolin or washing and cooking of BR with calcium hydroxide or calcium hydroxide and gypsum resulted in considerable reduction of alkali content; up to 75%. At the same time the reactivity of the BR was reduced but still being higher compared to fly ash already used in the cement industry.

Influence of Starkeya novella on Mechanical and Microstructural Properties of Cement Mortars

Cement-based materials are subject to degradation during their service life. Most of the structural failures have been associated with corrosion of the rebar due to chloride ingress, alkali aggregate reaction, and/or sulfate attack. Microbial activities, especially in waste water collection points such as sewer lines, may compromise the integrity of concrete structures. This study reports an experimental work carried out to determine the effect of Starkeya novella bacteria species on mechanical and microstructural properties of cement mortars. Mortar prisms were prepared from selected ordinary Portland cement (OPC) and Portland pozzolana cement (PPC) in Kenyan markets. Bacterial solution of 1.0 × 107 cell/mL concentration was used as either mix water, curing media, or both. Distilled water was used to prepare mortar prisms for control samples. Compressive strength was determined after the 7th, 28th, 56th, and 90th day of curing. Scanning electron microscopy (SEM) was tested on both bacterial and control mortar prisms after the 28th day of curing. Both PPC and OPC exhibited significant decrease in compressive strength for bacterial-prepared mortars as compared to controls. SEM analysis showed extreme erosion on the microstructure of the microbial mortars. This was denoted by massive formation of ettringite and gypsum which are injurious to mortar/concrete.

A Fundamental Study on the Potential of Alkali-Aggregate Reaction according to KS F 2545 and ASTM C 1260 Test Methods

Chemical experiment KS F 2545 and Physical experiment ASTM C 1260 has been accomplished to estimate the potential of alkali aggregate. Used for testing aggregate samples are forest aggregate and recycled aggregate which collected in Gangwon province Samcheok and Pyeongchang, Jeollabuk province Gimje and Kochang, and Gyeongsangnam province Goryeong. As the results of chemical experiment confirmed that if silicate rock and carbonate rock are mixed, reduction in alkalinity is increase. So it has been identified that case makes a disturb at the result of alkali aggregate reaction. In 9 out of the 62 aggregate samples check dissolved silica exceeding 100 mmol/ℓ. and mortar bar length increase rate confirmed that 5 of 9 chemical method aggregates were 0.1~0.2% and 2 aggregates were 0.2%. As a result of the alkaline aggregate reaction test using the chemical method and the mortar bar method, the aggregates showing alkali aggregate reaction are sandstone and tuff aggregates. Therefore, Alkali aggregate reaction tests are required to use clastic sedimentary rocks and volcanic pyroclastic rocks aggregates.

Long-Term Durability of Marine Reinforced Concrete Structures

The sustainability of reinforced concrete is critical, particularly for structures exposed to marine environments. Chlorides are implicated in causing or accelerating reinforcement corrosion and potentially earlier expensive repairs, yet there are many older reinforced concrete structures in good condition for many decades despite very high chloride levels at the reinforcement. The reasons for this are reviewed briefly, together with recent experimental work that better defines the role of chlorides. One is initiation of reinforcement corrosion but only through localized pitting at air-voids in concrete at the interface with the steel reinforcement. These tend to be small or negligible for high quality well-compacted concretes. The other role for chlorides has been shown, in experimental work, to accelerate the long-term loss of concrete alkali material. On the other hand, a review of practical experience shows that what has been termed chloride-induced reinforcement corrosion often is not that at all, but is the end-product of factors that impair the protective nature of the concrete. As reviewed herein, these include poor compaction, physical damage to concrete cover, concrete shrinkage, and alkali-aggregate reactions. The various observations presented are important for the proper understanding, analysis, and design of durable reinforced concrete structures exposed to chloride-rich environments.

Mineralogical Characterization of Historical Cement-based Mortars from the Rupnik Military Fortification Line

ABSTRACT This paper presents the results of cement-based mortars characterizations that were taken from rendered layers of military bunkers in the Rupnik Line. The Rupnik Line was conceived as a part of the fortified defence system protecting the Rapallo Border between the Kingdom of Italy and the Kingdom of Yugoslavia, established in 1920. The bunkers were built between 1938 and 1941, and the renders of various compositions were applied as a camouflage layer that merged the bunkers with the environment. Results of petrographic examination and microstructural and chemical analysis of the samples confirmed that locally available crushed dolomite or limestone sands were used as an aggregate in the mortars. As binders, pure Portland cement or a mixture of cement and ground granulated blast furnace slag were used. The selection of the aggregate and binder type in a particular mortar was based on the colour of the artificial stone produced. All samples with the dolomite aggregate show the presence of alkali-aggregate reactions, dedolomitization of the grains and secondary calcite formation in the cement binder, along with the Mg-Al, Mg-Si and Mg-Al-Si phase formations. In mortar compositions with a high Portland cement content, the presence of delayed ettringite formation was also confirmed.

Stochastic analysis of concrete dams with alkali aggregate reaction

Following a comprehensive literature survey, this paper will first address the theoretical underpinnings of stochastic modeling. An algorithm to model arch dam inhomogeneity in terms of characteristic length is presented next and is applied to assess the impact of concrete's elastic modulus and volumetric AAR expansion. Results are contrasted with both a single deterministic analysis, and a series of classical Monte Carlo simulations in which non-Gaussian stochastically varying properties are used.The impact of randomness in material properties on displacements, joint openings, and stresses are investigated. It is found that whereas mean values of these responses are for the most part little impacted, standard deviations exhibit a greater variation vis a vis simple Monte Carlo simulations. Furthermore, the safety is assessed through fragility surfaces, and meta-modeling. This study determined that whereas randomness may affect local results e.g. stresses, their impact may be neglected for globally averaged responses e.g. displacements.

FABRICAÇÃO DE CONCRETO AUTOADENSÁVEL COM UTILIZAÇÃO DE RESÍDUOS DE MARMORARIAS COMO ADIÇÃO MINERAL

RESUMO: O objetivo deste é determinar o percentual de substituição de cimento por resíduos de mármores/granitos (RMG) das marmorarias na fabricação de concreto autoadensável (CAA). A metodologia adotada foi a realização de vários ensaios laboratoriais: de caracterização; das propriedades reológicas, mecânicas, físicas e químicas do CAA. Foram aplicados dois superplastificantes, sulfonado e polimérico. Os agregados foram caracterizados por ensaios de granulometria, massa específica; massa unitária em estado solto; e massa unitária em estado compactado. Os RMG foram submetidos a ensaio de massa específica e análise de Fluorescência de Raios X. Como ensaios reológicos foram realizados: Espalhamento, T500, Funil V e Caixa L; e Ensaios de Resistência à Compressão e à Flexão, Absorção, Índice de Vazios, Massa Específica e análise de Reação Álcali Agregado (RAA), no estado endurecido. Os resultados mostraram-se eficazes com até 30% de substituição do cimento por RMG. No estado fresco esse CAA atendeu aos requisitos da NBR 15823 (ABNT, 2010), se comportando como concreto adequado para utilização nas aplicações correntes. No estado endurecido apresentou resistência à compressão de 35 MPa e resistência à flexão de 7,0 MPa, satisfazendo a NBR 15805 (ABNT, 2010), podendo também ser utilizado na produção de pavimentos de concreto e assim contribuindo para a redução de resíduos espalhados nas empresas, diminuição de danos ao meio ambiente e trazendo economia para a obtenção de CAA.

Effects of alkali-silica reaction on mechanical behavior of four-pile caps

ABSTRACT: The structural behavior resulting from alkali-aggregate reactions on four-pile caps was numerically studied using software based on the Finite Element Method. The cracking was analyzed in terms of reduction rates in the mechanical properties of the concrete (compressive strength, tensile strength and modulus of elasticity) as a consequence of the expansion induced by the alkali-aggregate reaction (AAR) referred to in the literature. One option for dealing with changes in mechanical properties, reported as influenced by the reactive aggregate type, environmental conditions and stress state, is to directly use the value of the properties of the material tested in the analysis, an approach adopted in the study and implemented in the analysis. From the results found in the analysis program the three main effects of AAR could be better understood: expansion, cracking and degradation of mechanical properties of concrete.

Diagnosis of alkali aggregate reaction in concrete dams: an Indian case study

Diagnosis of alkali aggregate reaction in concrete dams: an Indian case study

Vitrified and nonvitrified municipal solid wastes as ordinary Portland cement (OPC) and sand substitution in mortars

AbstractThis work aims to evaluate the potential suitability of nonvitrified and vitrified bottom ashes to serve as substitute materials for both OPC and sand in mortars on an industrial scale. Three bottom ashes were selected as OPC substitutes: one was vitrified inside the incinerator plant (W1‐C), one was carbonated under ambient conditions for 3 months (W2‐C), and part of the carbonated bottom ash was further washed with Ca(OH)2 (W2‐W‐C). Composition and phases of the bottom ash sources were assessed by XRF and XRD, respectively. Thereafter, mortars were prepared by replacing 10, 20 or 30 wt% of OPC with these bottom ashes. It was shown that even though Ca(OH)2 washing step (W2‐W‐C) led to an increment of the compressive strength in final mortars compared to the use of W2‐C, it failed to reach the mechanical performance of OPC. On the contrary, the use of vitrified bottom ashes (W1‐C) could lead to obtaining compressive strength comparable to that of standard mortar if added up to 10 wt%. Regarding the sand substitution, vitrified bottom ashes could reach suitable compressive strength when replacing 20 wt% of standard sand. The alkali aggregate reaction test confirmed the neutrality of substitution material added up to 50 wt%.

Wadi gravel – a new concrete aggregate in Qatar: Part 2 –Alkali aggregate reactivity

Deposits of Wadi gravel are available in many parts of the Gulf region, but not widely utilized as aggregate for concrete, mainly due to the possibility of internal sulfate attack, plus the perceived risk of alkali aggregate reactivity (AAR). This paper describes the investigations for AAR of the Wadi gravel in this case, as part of the wider study described in Part 1 of this paper. Wadi gravel from the Mekaines site in Qatar was subjected to petrographic analysis, plus the gel-pat and accelerated mortar-bar test methods. The AAR potential was found to be low to normal. The accelerated mortar-bar test exhibited ‘innocuous’ behaviour after 14 days of immersion in alkali solution. When separately testing the constituent rock types of the Wadi gravel, limestone and quartz returned innocuous results, while rhyolite, granite and quartzite returned potentially alkali silica reactive (ASR) results and some reaction was confirmed using post-expansion petrographic examination. Wadi gravel was classified as potentially reactive in the RILEM AAR-4.1 accelerated concrete prism test, but of ‘low reactivity’ in the BS 812-123 test over the longer period of 12 months. Overcoming the potential problems of gypsum content and AAR successfully provides a valuable local resource of Wadi gravel aggregate for concrete.

Durability of cement mortar-covered BFRP bars in simulated seawater environment

To assess the durability of basalt fibre-reinforced polymer (BFRP) bars used to reinforce concrete structures in ocean engineering, the evolution of the thermomechanical properties of cement mortar-covered BFRP bars immersed in simulated seawater environments was studied. The cover thicknesses were set as 10 mm and 20 mm, the immersion temperatures were room temperature (≈28 °C), 40 °C, and 60 °C, and the immersion media were an alkaline solution and distilled water. A set of bare glass fibre-reinforced polymer (GFRP) bars was used for comparison. After one year, the mechanical properties of the bare BFRP bars immersed in a 60 °C alkaline solution deteriorated the most, and the tensile strength decreased from 954.2 MPa to 762.3, 594.7, and 515.5 MPa for the bare BFRP bars and the 10 mm and 20 mm cement mortar-covered specimens immersed in distilled water at room temperature, respectively. The results indicated that alkalinity is a key factor causing the degradation of BFRP and that deterioration is more evident in large-sized cement mortar. In addition, an alkali–aggregate reaction (AAR) of SiO2 in the basalt fibre was evidenced by the presence of a white gel at the interface between the BFRP bars and cement mortar. Thus, AAR is detrimental to the mechanical properties of the cement mortar-covered BFRP specimens in the initial stage. With an increase in immersion time, the cement mortar layer exhibited a protective effect, particularly for the small-sized cement mortar-covered specimens. The BFRP bars are more durable than the GFRP bars owing to the higher fibre volume fraction of GFRP.

Durability study of concrete-covered basalt fiber-reinforced polymer (BFRP) bars in marine environment

To understand the durability of basalt fiber-reinforced polymer (BFRP) bars for the reinforcement of concrete structures applied in marine environments, BFRP bars with 20-mm concrete covers were immersed in ocean water or simulated seawater at room temperature (~23 °C), and the evolution of the thermomechanical properties was studied. A set of uncovered BFRP bars immersed in ocean water and laboratory accelerated simulated seawater (23 °C, 40 °C, and 60 °C) was investigated for comparison. After one year, the mechanical properties of the uncovered BFRP immersed in 60 °C simulated seawater showed the most degradation, followed by the concrete-covered BFRP in the laboratory immersion. Concrete-covered BFRP showed more deterioration than uncovered BFRP in the ocean water. The results indicated that the alkalinity is the key factor causing the degradation of BFRP, especially for standing water in the laboratory environment. In addition, an alkali-aggregate reaction (AAR) of SiO2 in basalt fiber was found at the interface between the BFRP bars and concrete. The degradation of the resin matrix and sizing led to the direct exposure of basalt fiber to alkaline solution, which established the foundation of the AAR.

Alkali Aggregate reaction in Dam Structures – a Review

Alkali – Aggregate Reaction is an unwanted reaction which occurs in concrete, mainly the area which is subjected to more moisture content. It occurs over time, between cement paste and silica. This in turn alters the expansion of the aggregate and often in an unpredictable way, which will result in loss of strength of concrete and also a complete failure. Hydro structures, mainly Dams store water, presence of moisture can cause such problem, comparatively more than the other structures. Normally, most of the dams had been constructed several years back and they still exist. The design was based on the environmental conditions prevailed at that period. But now the fast changing environmental aspects and industrial growth and technological development apart from global warming has severe impact on the life and performance of the dams. Dam Structures cannot be easily replaced, and the swelling can block spillway gates or turbine operations. The durability of dams has the impact on human life, society and the environment. To enhance the life and durability of the dams or hydro structures, several studies were made. There are two forms of Alkali Aggregate Reactions available, Alkali Silica Reaction and Alkali Carbonate Reaction and this paper reviews Alkali Aggregate reaction within concrete construction.

Alkali-aggregate reaction in alkali-activated cement concretes

The paper discloses the results of a study on structure formation processes in the interfacial transition zone “cement stone − aggregate” of the alkali-activated cement concretes. The results indicate the importance of the content of Al2O3 in the cement and aggregate. Together with components that are able to interact actively with alkalis in the presence of reactive SiO2, the processes taking place during the alkali-aggregate reaction can have weather destructive or constructive effect. The constructive effect is caused by incorporating the corrosion products into alkaline aluminosilicate compounds, thus retarding the internal corrosion of the concrete and providing the higher durability even in case of alkali-activated cements and alkali-susceptible aggregates with relatively high alkali content.

Investigation on durability of concrete exposed to chloride, sulfate attack and steel corrosion

In the present age, the concrete material is playing an increasingly important role in construction. But in the meantime, environmental features have serious damaging influence on the concrete. Consequently, this damage will decline the long-time persistence and serviceability of concrete structures. This review paper discusses recent researches activity on the permanence of concrete, including: a) main durability problem including sulfate attack, steel corrosion and alkali aggregate reaction, b) durability of concrete in nautical location such as seawater, groundwater, Salt Lake; and c) mix with effects of environmental items and mechanical loads on persistence of concrete. This report is based on results of many realistic experiments which happened by scientist. Consequently, it’s important to follow these methods to improve service life of concrete and durability would be superior.

Durability of recycled aggregate concrete incorporating slag

This paper presents the results of experimental research on the durability and performance of various mixes of recycled aggregate concrete (RAC) incorporating 25% ground-granulated blast-furnace slag (GGBS) as a cement replacement. The compressive strength, drying shrinkage, water penetration, water absorption, alkali–aggregate reactivity and sulfate content of the concrete mixes were tested. The results indicated that the addition of mineral slag improved the mechanical properties and durability characteristics of the RACs. The addition of 25% GGBS proved to be efficient in reducing water absorption, alkali–silica reactivity and sulfate attack in RAC. However, the test results showed that the introduction of 25% GGBS is not effective enough to prevent the excessive expansion of the alkali–carbonate reaction in RAC after 1 year of testing. Furthermore, it has an adverse impact on resisting the water penetration and drying shrinkage of the RAC mixes.