Mortar Bar Research Articles

Impact of pore solution concentration on the accelerated mortar bar alkali-silica reactivity test

The accelerated mortar bar test (AMBT), commonly used for evaluating the potential alkali-silica reactivity (ASR) of aggregates, is unreliable in some cases. Likely, this lack of reliability is due in part to the 80 °C temperature and the 1 N NaOH storage solution specified in the test differing significantly from field conditions. Therefore, the influence of temperature and storage conditions on pore solution composition was studied. The AMBT procedure was modified accordingly and improvements in the accuracy were assessed against the results of the concrete prism test at 38 °C (CPT) and the accelerated concrete prism test at 60 °C (ACPT), as well as known field performance. Modifying the temperature of the standard AMBT to 60 °C and the storage solution to 0.65 N KOH + 0.15 N NaOH, for more representative pore solutions was found to only improve the accuracy for aggregates exhibiting pessimum behaviour.

An attempt to apply a slag binder with zeolite in mining construction. Durability and hardness

The paper presents comparative results of strength tests on mortars, hardness of pastes and their microscopic observations. The focus was on alkali activated ground granulated blast furnace slag (GGBFS) to which the zeolite was introduced. Zeolite positively affects the rheological properties, densifies the microstructure by reducing its permeability and binds Ca(OH)2. It causes lower susceptibility of the binder to corrosion, which can be affected by mine mineralized waters or brines flowing from the salt beds. To increase the mechanical properties, polymer scattered reinforcement was used, which does not corrode in contact with saline waters, contrary to steel reinforcement. The paper presents the results of: bending strength and compression strength of mortar bars made of slag (S2), slag with zeolite (S3), slag with zeolite and polymer fibers (S5); the Vickers indenter tests results of slag pastes of S2 and S3 as well, up to 90 days of hydration. The 90 day compressive strength was 64.0 MPa; 27.7 MPa and 64.7 MPa, and bending strength: 6.4 MPa; 2.9 MPa and 6.0 MPa, respectively for S2, S3, S5. The Vickers indenter test at HV 1 was as follows: on average 27.04 MPa and 36.69 MPa, respectively for S2 and S3. Microstructure observations were carried out in SEM. The obtained results require further research work.

Resistance of selected aggregates from igneous rocks to alkali-silica reaction: verification

The paper presents investigations into the reactivity of aggregates from igneous rock, carried out in accordance with the procedures contained in the GDDKiA General Technical Specification "Concrete pavements". The aim of the investigations was evaluation of the suitability of the aggregates for road structures and pavements built using cement based concrete technology. Aggregates produced from extrusive rocks (basalt, melaphyre and porphyry) and from intrusive rocks (granite and gabbro) were analysed. The mineral composition of the aggregates was evaluated with regard to their reactive SiO2 content. Expansion tests on mortar bar and concrete prism specimens with analysed aggregates and a microscopic analysis of the alkali-aggregate reaction products were carried out. A considerable amount of reactive minerals: chalcedony, tridymite and microcrystalline quartz and volcanic glass were found in the grains of the porphyry and melaphyre aggregates. On the basis of the conducted investigations the two aggregates made of igneous rocks (melaphyre and porphyry) were classified into category R1 (moderately reactive). The basalt aggregate, the granite aggregate and the gabbro aggregate were assigned to category R0 (non-reactive).

Effect of fly ash and limestone powder on inhibiting alkali aggregate reaction of concrete

Abstract The alkali aggregate reaction (AAR) about the aggregate marked with W1# was studied by using of four kinds of methods, including accelerated mortar bar test (AMBT), mortar bar length test (MBLT), concrete prism method (CPM) and rock column method (RCM). AMBT showed that the expansion ratio of the specimens at 14 days was 0.200%, and the expansion ratio at 28 days was 0.404%; MBLT showed that the expansion ratio at 3 months was higher than 0.050%, and the expansion ratio at 6 months was higher than 0.100%; CPM showed that the expansion ratio at 39 weeks was higher than 0.040%. These studies above indicated that W1# aggregate was the aggregate with potential alkali-silica activity. RCM tests showed that the aggregate doesn’t have potential alkali-carbonate activity. The inhibiting experiments showed that the expansion ratio at 14 days and 28 days were less than 0.10% by adding more than 45% (Wt/%) limestone powder or adding 15% (Wt/%) fly ash, meanwhile, the expansion ratio at 14 days and 28 days were all less than 0.10% after adding 15% (Wt/%) limestone powder and 30% (Wt/%) fly ash or adding 25% (Wt/%) limestone powder and 25% (Wt/%) fly ash, respectively. Mesh structures were formed by the hydration products in the micro structure, and no micro cracks and the white flocculent products could be observed inside and outside of the samples. All the results above confirm that AAR of the aggregate was inhibited effectively, and it will play the useful role in AAR research.

An Accelerated Test Method to Evaluate Cementitious Mixtures Subjected to Chemical Sulfate Attack

Abstract External sulfate attack continues to be a major threat to the long-term durability of concrete structures. Soil or water containing sufficient levels of sulfates can penetrate and chemically react with the hydrated cement compounds, leading to volumetric expansion, and in severe cases, softening of the hardened cementitious paste. While ASTM C1012, Standard Test Method for Length Change of Hydraulic-Cement Mortars Exposed to a Sulfate Solution, is the most widely accepted performance test method used to access the sulfate resistance of cementitious binders, the test requires at least six months and often up to twelve months to perform. This article presents a new accelerated method that places mortar bar specimens under high-vacuum while immersed in sulfate solution to accelerate the penetration and diffusion of sulfates in the specimens and therefore, the degradation and measured linear expansion of the specimens. Expansion, mass change, and visual degradation were assessed over time on mortar specimens immersed in a 5 % and 0.89 % sodium sulfate solution (Na2SO4) and subjected to the vacuum saturation procedure. Expansion results are compared with companion mortar bars that followed the ASTM C1012 method without vacuum saturation. When compared with the current ASTM method, the new test method showed a significant acceleration in the rate of expansion with severe visual deterioration observed two to three times quicker. Visual degradation and measured expansion occurred more rapidly for specimens subjected to the accelerated method and immersed in 5 % Na2SO4; however, mixtures subjected to the accelerated method and immersed in 0.89 % Na2SO4 still showed much faster expansion than companion specimens tested according to ASTM C1012 in 5 % Na2SO4.

Performance of recycled soda–lime glass powder in mitigating alkali–silica reaction

Recycled soda–lime glass powder (SLGP) is a valuable supplementary cementitious material. However, it has a high alkali content, and its effectiveness in mitigating the alkali–silica reaction (ASR) is uncertain. In this study, the ASR performance of SLGP was evaluated using the accelerated mortar bar test (ASTM C 1567) and the concrete prism test (ASTM C 1293). It was determined that a sufficient dosage of SLGP can mitigate ASR according to ASTM C 1567, and that finer SLGP is more effective. Meanwhile, the 2-year concrete prism test showed that the same type, fineness and dosage of glass powder as tested by C 1567 does reduce ASR, but not sufficiently and below the ASTM failure threshold. Pore fluid composition monitoring revealed that SLGP, over time, serves as a net contributor to the pore solution alkalinity, but these alkalis are released slowly. Overall, SLGP can reduce ASR, albeit insufficiently and temporarily. This ASR reduction is likely through a combination of reduced pore solution pH at early ages (due to cement dilution) and reduced portlandite content and transport properties at later ages (due to pozzolanic reaction). Long-term ASR testing is necessary to determine if and at what dosage a glass pozzolan may be able to control ASR sufficiently.

Alkali-silica reactivity of basaltic aggregates of Mesopotamia Argentina: case studies

This work consists of two stages; first, studies were conducted to evaluate the potential reactivity of crushed material (6–20 mm fraction) from two quarries (named A and B) producing basaltic aggregates in the northeast of Argentina (Mesopotamia region, province of Corrientes). The studies included petrographic analysis, identification of expandable clay by X-ray diffraction, and standardized physical tests on mortar bars and concrete prisms to evaluate their potential reactivity. Also, dissolved silica was determined according to the chemical test method. Although the studied aggregates cannot be qualified in the same way based on the results of the physical tests, there is a direct relationship between the glass and expandable clay content in the samples (quarry A aggregate > quarry B aggregate) and their behavior in the physical and chemical tests (higher values for aggregates A). In the second stage, two structures of the province of Corrientes were studied: an urban pavement (made with aggregate A) and an airport runway (made with aggregate B), both with signs of alkali-silica reaction (ASR). A visual survey was carried out and concrete cores were extracted. On the latter, physical tests, petrographic studies, and SEM-EDS determinations were performed to identify reaction products. In the urban pavement, aggregate A, used as coarse aggregate, and the presence of siliceous sandstones rich in chalcedony and microcrystalline quartz in the fine aggregate would have contributed to ASR development, while in the airport runway, the initial deterioration would have favored the ASR as a secondary process.

Effectiveness of 3 different supplementary cementitious materials in mitigating alkali silica reaction

Abstract A detrimental chemical reaction between alkali from cement and reactive silica from aggregates can occur in concrete that affects concrete durability and such a reaction is called “Alkali Silica Reaction” (ASR). Many different supplementary cementitious materials (SCMs) have been utilized to mitigate ASR in concrete with varying degree of effectiveness. This investigation studied the effectiveness of 3 SCMs, clay brick powder, glass powder, and natural zeolite, in mitigating alkali silica reaction. Accelerated mortar bar test method (AMBT) according to ASTM C 1260 was employed to study the effectiveness of SCMs in reducing ASR expansion in mortar bars that consisted of a local reactive volcanic aggregate. Cement replacement level of 20 percent by weight was chosen to study the effectiveness of each SCM. It was found that all three SCMs were able to reduce expansion of the mortar bars to under acceptable limit. Natural zeolite was found to be the most effective, followed by brick powder and glass powder. It was postulated that the effectiveness generally increased with the increasing amount of Si in mortar, as well as a decrease in Ca to Al ratio.

On utilization and mechanisms of waste aluminium in mitigating alkali-silica reaction (ASR) in concrete

Alkali silica reaction (ASR) is one of the most commonly occurring durability issues in concrete structures. In this study, the feasibility of using waste aluminium in bit, powder and dissolved forms as a sustainable alternative to mitigate ASR was investigated. The accelerated mortar bar test was adopted for expansion measurement and mitigation mechanisms were explored with reactive glass dissolution, pore solution and microstructural analyses. Both aluminium bits and aluminum powder at various volume fractions were found to be effective in mitigating ASR, mainly attributable to dissolution control of amorphous silica through integration of [Al(OH)4]- into the silica framework and electrostatic repulsion of OH− at reactive sites. However, the effectiveness of the dissolved aluminum form in controlling ASR was diminished with time due to a ready integration into hydration products. This calls for an investigation into the long-term effectiveness of the proposed mitigation strategies. Also, a higher porosity of concrete due to gas evolution and the resulting adverse effects on mechanical properties would have to be resolved before a possible implementation of the mitigation approach for concrete structures.

Comparing the alkali-silica reaction mitigation potential of admixtures by using different accelerated test methods

This study provides a comparative study of the accelerated mortar bar (ASTM C1260-14 and ASTM C 1567-13) and RILEM AAR-4 test methods. They were used to evaluate the alkali-silica reaction (ASR) mitigation potential of supplementary cementitıous materials (SCMs) and lithium salts. For this purpose, 96 mixtures with two different reactive aggregates were prepared and analyzed by the accelerated mortar bar test (AMBT) and RILEM AAR-4 method. The effect of steam curing was also determined. Despite the factors such as severe test conditions of the AMBT and alkali leaching challenge in the AAR-4, in some cases, meaningful relations were observed between these accelerated test methods.

EFFECTS OF ALUMINIUM ADDITION ON INHIBITION OF CONCRETE EXPANSION RESULTED FROM ALKALI SILICA REACTION (ASR)

Alkali-silica reaction (ASR) is one of the major causes of expansion, which ultimately leads to failure in concrete. When reactive concrete is subjected to humidity, alkali silicate hydrate gel (ASR gel) is formed. The swollen ASR gel exerts pressure and creates cracks in the concrete structure. This study, thus, aimed at inhibiting concrete expansion which was caused by the ASR reaction, by creating pores. To achieve pore formation, aluminium powder was used as an air entrainment agent. Mortar bars with aluminium content of 0.05, 0.1, 0.15 and 0.2 weight percent of cement was tested according to the ASTM C1260: Standard Test Method for Potential Alkali Reactivity of Aggregates. The results indicated that a larger quantity of entrained pores was achieved at higher aluminium content. The results also showed that when tested according to the ASTM C1260, concrete expansion was reduced as the aluminium content was increased. Microstructural analysis revealed that the entrained pores accommodated spaces for ASR gel, resulting in the decline of concrete expansion.

Reactivity tests for supplementary cementitious materials: RILEM TC 267-TRM phase 1

A primary aim of RILEM TC 267-TRM: “Tests for Reactivity of Supplementary Cementitious Materials (SCMs)” is to compare and evaluate the performance of conventional and novel SCM reactivity test methods across a wide range of SCMs. To this purpose, a round robin campaign was organized to investigate 10 different tests for reactivity and 11 SCMs covering the main classes of materials in use, such as granulated blast furnace slag, fly ash, natural pozzolan and calcined clays. The methods were evaluated based on the correlation to the 28 days relative compressive strength of standard mortar bars containing 30% of SCM as cement replacement and the interlaboratory reproducibility of the test results. It was found that only a few test methods showed acceptable correlation to the 28 days relative strength over the whole range of SCMs. The methods that showed the best reproducibility and gave good correlations used the R3 model system of the SCM and Ca(OH)2, supplemented with alkali sulfate/carbonate. The use of this simplified model system isolates the reaction of the SCM and the reactivity can be easily quantified from the heat release or bound water content. Later age (90 days) strength results also correlated well with the results of the IS 1727 (Indian standard) reactivity test, an accelerated strength test using an SCM/Ca(OH)2-based model system. The current standardized tests did not show acceptable correlations across all SCMs, although they performed better when latently hydraulic materials (blast furnace slag) were excluded. However, the Frattini test, Chapelle and modified Chapelle test showed poor interlaboratory reproducibility, demonstrating experimental difficulties. The TC 267-TRM will pursue the development of test protocols based on the R3 model systems. Acceleration and improvement of the reproducibility of the IS 1727 test will be attempted as well.

Compressive strength and durability properties of roller-compacted concrete pavement containing electric arc furnace slag aggregate and fly ash

This study investigates the effects of electric arc furnace (EAF) slag aggregate and fly ash on compressive strength and durability properties (i.e. water absorption, abrasion resistance, and sulfate resistance) of roller-compacted concrete pavement (RCCP). The EAF slag aggregate as natural aggregate substitution was used at three levels (i.e. 0%, 50%, and 100%) and cement was replaced by fly ash at three ratios (i.e. 0%, 20%, and 40%). The EAF slag aggregate used in this study was exposed to outdoor condition for several months to reduce the volume instability. The RCCP mixing proportions were determined by soil compaction method. The compressive strength of RCCP was examined at 3-, 7-, 28-, and 91-day age. Meanwhile, the water absorption, abrasion resistance, and sulfate resistance of RCCP at 91-day age were used to study the durability properties. Furthermore, the length change of mortar bars made with EAF slag aggregate was measured to evaluate the expansive potential of EAF slag caused by autoclave condition and alkali-silica reaction (ASR) condition. Additionally, X-ray diffraction analysis was offered to identify the crystalline phases of mortar patterns under autoclave and ASR testing condition. The results presented that the compressive strength and sulfate resistance of RCCP containing EAF slag aggregate declined slightly, whereas the water absorption and abrasion resistance increased in comparison to those of traditional RCCP. Besides, the use of fly ash as cement substitution improved the compressive strength of slag-RCCP at long-term age. A replacement of 20% fly ash provided the slag-RCCP fulfilling the strength and durability requirements for pavement. In addition, the expansion in terms of length change of mortar bars indicated that EAF slag aggregate after the proper treatment performed the volume stability under the autoclave condition and ASR test.

A comparative study between ASTM C1567 and ASTM C227 to mitigate alkali‐silica reaction

The primary objective of this study was to evaluate the two different widely adopted test methods such as american society for testing and materials (ASTM) C1567 “accelerated mortar bar method” and ASTM C227 “mortar bar method” to identify the alkali‐silica reaction (ASR) of ferronickel slag fine aggregates. The ASR mitigation measure was assessed by the application of supplementary cementing material such as fly ash. During the experimental investigation visual inspection, mortar bar expansion and tensile strength measurements were evaluated. The test results point out that mortar bar method was unsuccessful to identify the ASR due to significant alkali leaching during the experiment. On the other hand, accelerated mortar bar method was successful to identify ASR and able to determine the safe dosage of fly ash to mitigate this deleterious expansion.

Role of test method in detection of alkali–silica reactivity of concrete aggregates

The risk of alkali–silica reaction of concrete aggregates in many parts of the world remains largely unexplored. In particular, a suitable approach for testing aggregates with marginal to moderate alkali–silica reactivity has not been clearly identified. In this study, the mineralogical compositions of aggregates from five different quarries were investigated. Mortar bar expansion for these aggregates was tested as per the guidelines of both C 227 and C 1260. Although the tested aggregate sources proved non-reactive under ASTM C 227 test conditions, ASTM C 260 identified one group of aggregates as potentially reactive. Scanning electron microscopy imaging confirmed that two sources of aggregates were reactive. The compressive and flexural strength test results of aged specimens with reactive aggregates indicated that the strength reduction of those subjected to 1 month of ASTM C 260 exposure was similar to those of specimens under 6 months of ASTM C 227 exposure. Based on the experimental results, it appears that aggregates with potential alkali–silica damage may be characterised as non-reactive if the appropriate test method is not adopted. The findings indicate that the ASTM C 1260 procedure is more effective in determining the reactivity potential of marginally to moderately reactive aggregates.

Influence of the Quartz Deformation Structures for the Occurrence of the Alkali⁻Silica Reaction.

Defects in the crystalline structure of quartz facilitate the connection with the alkali hydroxides, since under a high alkalinity condition (e.g., in concrete), the Si-O bonds of quartz are easily broken. This study set out to investigate the influence of the deformation structures of quartz on its susceptibility to the alkali–silica reaction. A granite, a protomylonite, and a mylonite were selected for this study. Using optical microscopy, the quartz grains contained in these rocks were quantified and their texture characterized. The quartz samples extracted from the rocks were analyzed by magnetic nuclear resonance, to evaluate their potential for dissolving silica as well as changes in their atomic scale before and after the reaction with alkali hydroxides. These analyses were compared with the results of the accelerated mortar bar test. The study showed that the quartz with intense undulatory extinction and deformation bands denotes the most favorable condition to the development of the alkali–silica reaction. However, on an atomic scale, the slightly deformed grains were highly prone to react. Thus, in a high alkalinity condition, over a long period of time, any quartz tends to develop the alkali–silica reaction, regardless of the deformation degree of the grain.

Experimental and numerical investigation of the alkali-silica reaction in the cement-based materials

The main subject of this paper is the investigation of the influence of the alkali-silica reaction on the microstructure and the transport properties of the cement-based materials. In the experimental research, mortar bars prepared with two different aggregates and stored in conditions of various alkali content were examined. Influence of the reaction on the microstructure of the material was investigated using mercury intrusion porosimetry, water capillary suction test and water vapour adsorption test. Mathematical model of the alkali diffusion and the reaction development is presented. It allows to take into consideration the influence of alkali concentration and aggregate sizes on the reaction development. The numerical code was developed using the finite element, finite difference and Newton-Raphson methods. Good accordance of the results obtained using the proposed model with the experimental data available in literature was obtained.

Effect of particle size of rice husk ash (RHA) in mitigating alkali silica reaction (ASR) in concrete pavement

Alkali-silica reaction (ASR) is considered as a major concern of distresses in concrete pavements and barriers in different locations across the state of Arkansas. Such premature distresses pose a significant increase in pavement life cycle cost. On the other hand, a large amount of rice husk ash (RHA) is produced in Arkansas, which is treated as an agricultural waste. In this study, different amounts (0, 10 and 20%) of three RHA samples with nominal sizes of 600 μm (600-RHA), 150 μm (150-RHA) and 44 μm (44-RHA), and a Class C fly ash (CFA) were used to observe the effect of gradation in ASR. Mortar bars were prepared and tested as per ASTM C1567. Test results revealed that finer RHA reduced the ASR expansion of the mortar bars. Both 600-RHA and 150-RHA contributed to significant expansion due to their bulk particle size. A 10% 44-RHA and a 10% CFA were found to be the optimum. In comparison to the Control, the 10% 600-RHA and 150-RHA samples expanded the bars by 101% and 40%, respectively and the 10% 44-RHA and CFA decreased the expansion of mortar bars by 81% and 95%, respectively. Furthermore, incorporation of RHA in the concrete pavement will reduce the pavement construction and maintenance cost.

Effects of alkali dosage and silicate modulus on alkali-silica reaction in alkali-activated slag mortars

The effects of silicate modulus and alkali dosage on alkali-silica reaction (ASR) of alkali-activated slag (AAS) mortars are investigated under accelerated mortar bar testing conditions as specified in ASTM C1260. At a given alkali dosage, an intermediate silicate modulus with respect to highest ASR expansion is observed, which increases from 1.0 to >2.0 with increase of alkali dosage. The effect of silicate modulus on ASR expansion is found to be governed by the pore solution alkalinity. At a given higher silicate modulus such as 1.5 and 2.0 at 14 day, the ASR expansion tends to increase with increase of alkali dosage, whereas it decreases with increase of alkali dosage at a given lower silicate modulus such as 0–0.5 at 28 day. The mechanism governing the effect of alkali dosage on ASR expansion is more complicated and cannot be explained by only the pore solution alkalinity.

EFFECT OF GRADATION AND REPLACEMENT LEVEL ON ALKALI-SILICA REACTIVITY OF MINERAL FILLERS

Mineral fillers are used in concrete for a number of reasons, which include achieving self-consolidation properties. Different fillers are available depending on the type of the original rock. Alkali-silica reaction might occur if the filler is produced from a reactive rock. The present research focuses on evaluating the applicability of the current accelerated mortar bar test, described in ASTM C1260 and CSA A23.2-25A, in evaluating their reactivity. Three different fillers are used: a calcium-carbonate filler, a carbonate silica filler with 27% SiO2, and a siliceous filler produced from reactive aggregate. Two different gradations of the filler obtained from reactive aggregate are tested: 1) Gradation finer than 75 µm; 2) Gradation with 30% passing 150 µm sieve but is retained on 75 µm sieve and remaining 70% passing 75 µm. Results showed that the calcium-carbonate filler and the carbonate silica filler did not show any expansion higher than the non-reactive sand, while the filler obtained from reactive aggregate did not show expansion higher than the control at 14 days for both gradations, with the expansion showing at later age. This might be due to the high surface area of fillers and the reduced permeability affecting the rate of expansion. Hence, the need to extend the testing period beyond the 14-day specified in the standard to be able to see the expansion.