Expansion Of Mortar Bars Research Articles

Long-term behavior of mortars experiencing delayed ettringite formation

Ettringite formation is an expansive reaction that causes cracking in the hydrated cementitious materials. This research has investigated the mechanisms of ettringite formation by examining the chemical and physical structure of the reactants and products involved in the process of late age (over 15 years) ettringite formation, and subsequent expansion and cracking. For this, seven different types of commercially available cement with their unique composition, and an elevated heat curing temperature of up to 100 °C were applied. The physical expansion of mortar bars due to delayed ettringite formation was monitored by the length change comparator. Environmental scanning electron microscopy (ESEM) was used to qualify and quantify changes in the microstructure and chemical composition of the cementitious matrix. Results revealed that the high-temperature heat curing accelerated the onset of expansion but limited the over-magnitude of the expansion. Results also revealed that the expansion may take years to initiate, likely due to a critical pore size threshold necessary to induce stresses. If expansion is delayed, the expansion magnitude is greater than those that expanded immediately.

The pH test technology suitable to evaluate content of hazardous electric arc furnace oxidizing slag in fine aggregate

In this study, a standard pH test procedure, based on the high alkalinity of electric arc furnace oxidizing slag, was developed for rapid content evaluation of potentially hazardous slag in the fine aggregate and recommended standards are further proposed. The advantages of the developed procedure include easy equipment acquisition, simple test method, short time, and high accuracy. This study found that sample size, water source, and filtrate process were the factors affecting the pH test accuracy. In the test, the pH increased with a decrease in the aggregate size when the proportion of electric arc furnace oxidizing slag in aggregate was fixed, especially when the aggregate size was less than 0.225 mm. Upon comparison of the results of autoclaved mortar bar expansion tests, a good logarithmic relationship was observed between pH and electric arc furnace oxidizing slag content. It is suggested that pH 9.0 could be used as the standard to determine excessive electric arc furnace oxidizing slag in fine aggregate.

Effects of desalinated sea sand on the alkali–silica reaction of seawater and sea sand concrete

The application of seawater and sea sand concrete (SWSSC) can reduce the construction period and cost of island infrastructure, but it may also bring the risk of alkali–silica reaction (ASR) owing to the presence of alkali ions in seawater and sea sand. To compare the characteristics of ASR between SWSSC and seawater and desalinated sea sand (DSS) concrete, the properties and the ASR products of mortar bars with different DSS content were studied. When the DSS proportion increased from 0% to 100%, the sodium (Na+), potassium (K+) and calcium (Ca2+) ion concentration of the specimens decreased by 22.6, 2.0 and 45.1 mg L−1, respectively, the pH decreased by 0.05 and the expansion of mortar bars was reduced by 0.16%. Desalination of sea sand could not eliminate the risk of ASR of SWSSC completely. The 14 days expansion of mortar bars with 100% DSS was 0.13%, and the precursors of ASR-P1 were observed by SEM. The experimental results of micriscopic tests all showed that with the increase of DSS proportion, the content of Na-shlykovite and ASR-P1 were reduced. A small amount of magnesium (Mg) in ASR products was detected. This study can provide a basis for the application of SWSSC in island infrastructure.

Petrographic Evaluation of Aggregate from Igneous Rocks: Alkali–Silica Reaction Potential

A thorough petrographic evaluation of aggregates from igneous rocks in terms of their alkali–silica reaction (ASR) potential is crucial in ensuring the durability and long-term performance of concrete structures, especially those where access to additional alkalis is possible, such as from de-icing agents. The aim of the research was to assess the potential reactivity of aggregates from igneous rocks, as only such aggregates are used for concrete airport pavements in Poland. Petrographic analysis was conducted to identify the reactive minerals in the aggregate, and it was extended by quantitative image analysis. The strained, microcrystalline and cryptocrystalline quartz were found to be reactive components but significantly differed in content. It was found that aggregates from igneous rocks were characterized by different susceptibility to ASR and that methods to mitigate the occurrence of ASR should be considered to be used in airfield concrete. A relationship between the content of analyzed reactive minerals and the expansion of mortar bars in AMBT, as well as of the concrete prism in the CPT method, was revealed.

Improving Concrete Infrastructure Project Conditions by Mitigating Alkali–Silica Reactivity of Fine Aggregates

Alkali–silica reactivity (ASR) is one of multiple reactions responsible for premature loss in concrete infrastructure service life. ASR results in the formation of expansive, white-colored gel-like material which results in internal stresses within hardened concrete. ASR-induced stresses result in concrete cracking, spalling, and increased reinforcement steel corrosion rates. The main objective of this research is to improve the conditions of concrete infrastructure projects by mitigating ASR’s damaging effect. The expansion of accelerated mortar bars poured using fine aggregates collected from different sources is measured versus time to evaluate the aggregates’ reactivity. Different percentages of supplementary cementitious materials (SCMs), including class C fly ash and microsilica, were used in remixing mortar bars to evaluate the efficiency of different types of SCMs in mitigating mortar bar expansion. The research findings showed that SCMs can mitigate ASR, thus decreasing mortar bar expansion. The efficiency of SCMs in ASR mitigation is highly dependent on the incorporated SCM percentage and particle fineness. Silica fume, having the smallest particle size, displayed higher rates of ASR mitigation, followed by fly ash. The outcomes of this research will assist design engineers in avoiding future losses due to ASR cracking in concrete infrastructure projects, and reduce the excessive need for maintenance, repair, and replacement activities.

Influence of Calcination Temperature and Amount of Low-Grade Clay Replacement on Mitigation of the Alkali-Silica Reaction.

Results of experimental investigation on the mitigation of alkali-silica reaction (ASR) by low-grade calcined clay are presented. Domestic clay with an Al2O3 content equal to 26% and SiO2-58% was used. The calcination temperatures were as follows: 650 °C, 750 °C, 850 °C and 950 °C, which were chosen much more widely than presented in previous studies. Pozzolanity of the raw and calcined clay was determined with the Fratini test. The performance of calcined clay to mitigate ASR was evaluated according to ASTM C1567 using reactive aggregates. A control mortar mixture was prepared with 100% Portland cement (Na2Oeq = 1.12%) as a binder with reactive aggregate, and test mixtures were made with 10% and 20% of calcined clay as a cement replacement. The microstructure of the specimens was observed on the polished sections using scanning electron microscope (SEM) operated in backscattered mode (BSE). The results of expansion of mortar bars with reactive aggregate showed that replacing cement with calcined clay reduced the expansion of the mortar bars. The greater the cement replacement, the better results in terms of ASR mitigation. However, the influence of the calcination temperature was not as clear. The opposite trend was found with the use of 10% or 20% calcined clay.

Effect of nano materials on cementitious mortar composites exposed to sulphate attack

Nanomaterials, owing to high surface area and nanoscale size, have unique physical and chemical properties that can be engineered with construction material to achieve novel properties. As such, the present study examines stand-alone and the synergetic effect of incorporating nanomaterials in cementitious mortars subjected to an aggressive environment. For stand-alone effect nano-silica was considered, and for synergetic effect nano-silica along with nano-alumina were considered. Specimens were cured in potable and sulphate water to examine their comparative strength and durability performance for various duration. Strength parameters, for example, compressive strength and flexural strength were examined. Experiments such as water absorption, sorptivity, and mortar bar expansion were conducted according to American Society of Testing Materials (ASTM) standards. For the hydrated cementitious mortar products, scanning electron microscopy (SEM) analysis was performed. Research examination revealed cementitious composites with enhanced strength and durability, especially specimens with nano-silica particles. These results were also evident from microstructural analysis for the hydrated composite cement mortar products. Therefore, it is possible to develop mortars as smart mortars by engineering nano-particles into the mix.

Test methods for performance-based evaluation of concrete containing iron sulfide-bearing aggregates: Development and application

Iron sulfide-bearing aggregates are susceptible to oxidation reactions that can lead to an internal sulfate attack in concrete, causing severe concrete distress. Appropriate performance-based evaluation methods are required to formulate guidelines to solve these issues. Unfortunately, the current standards and specifications do not comprehensively include such evaluation methods. The present study attempted to develop a set of test methods to evaluate the performance of concrete containing iron sulfide-bearing aggregates. These methods include acceleration of the oxidation process, evaluation of expansion and rusting, and assessment of the severity of pop-outs and map cracks. An accelerated mortar bar expansion test was used to measure the expansion. A storing temperature of 60 °C, 80 ± 5% RH, and wetting and drying cycles of 7 cycles per two weeks (6% NaOCl or H2O with oxygen added through the pump while submerged) were found to be particularly successful for accelerating the oxidation process in the laboratory. An image processing method based on the “Otsu technique” was used to quantify rusting. The severity of the pop-outs was assessed using the frequency and average area of the pop-outs. The average crack width and total length of cracks per unit area computed using an image processing technique were also used to appraise the severity of the map crackings. The developed test methods were applied to assess the effectiveness of surface treatments with distinct functional mechanisms in controlling the oxidation rate. Surface treatments with a crystalline waterproof system covered with the acrylic polymer coating exhibited outstanding performance.

Alkali–Silica Reactivity Potential of Reactive and Non-Reactive Aggregates under Various Exposure Conditions for Sustainable Construction

The alkali–silica reaction (ASR) is a primary cause for premature concrete degradation. An accelerated mortar bar test is often used to access the detrimental phenomena in concrete caused by the ASR of aggregates. However, this test requires a certain environmental conditioning as per ASTM C1260. The objective of this study is to explore the effects of the cement alkali content, exposure solution concentration, temperature, and test duration on mortar bar expansion. Factorial experimental design and analysis was conducted to delineate the effects of the individual factors as well as their interaction. Five different aggregates with various mineralogical properties were used, representing reactive and non-reactive aggregates. Various dosages of cement alkalis (0.40, 0.80, and 1.20 Na2Oe), sodium hydroxide (NaOH) solution concentrations (0.5, 1.0, and 1.5 N), and temperature (40 °C, 80 °C, and 100 °C) were the studied variables. Mortar bar expansion was measured at 3, 7, 14, 21, 28, 56, and 90 days. Mortar bars incorporating Jhelum aggregates incurred expansion of 0.32% at 28 days, proving to be reactive aggregates as per ASTM C1260. Similarly, specimens incorporating Taxila aggregates showed expansion of 0.10% at 28 days, indicating non-reactive nature. It was observed that specimens with Sargodha aggregates showed expansion of 0.27% at 28 days for 0.50 N NaOH solution concentration compared to 0.31% expansion for identical specimens exposed to 1.5 N solution. Moreover, expansion increased with exposure duration for all the tested specimens. Experimental results showed that the cement alkali contents had relatively lesser effect on expansion for 1.0 N NaOH; while, in the case of 0.5 N and 1.5 N NaOH, the cement alkali had a significant effect. It was noted that expansion increased with an increase in the temperature. Jhelum aggregates showed 28-day expansion of 0.290% when exposed to 40 °C, but at a temperature of 100 °C, expansion increased to 0.339%. Factorial analysis revealed that the exposure solution had a major contribution towards the expansion of mortar bar specimens. This study highlights the contribution of various exposure conditions on the ASR expansion, which leads to a decisive role in selecting the aggregate sources for various applications and exposure conditions leading to sustainable construction.

Effect of spent bleaching earth ash on sulphate attack resistance of concrete

One of the severe durability problems of concrete is sulphate attack. Sulphate attack can cause expansion of concrete due to the formation of gypsum and ettringite. Recently, spent bleaching earth ash (SBEA) is being used as a partial cement replacement in concrete. In this study, the effects of unground SBEA (USBEA) and ground SBEA (GSBEA) on sulphate attack resistance on concrete in terms of expansion of mortar bar and loss in compressive strength of concrete exposed to 5% sodium sulphate solution were determined. The SBEA was ground in a planetary grinding ball mill for 30 min to obtain a finer particle size. The expansion of mortar bars exposed to sulphate conditions containing USBEA and GSBEA was evaluated for 6 months according to ASTM C1012. Meanwhile, the compressive strength of concrete containing USBEA and GSBEA against sulphate attack was determined at 28 and 90 days. It was found that the expansion of mortar bars containing GSBEA was the lowest (0.01%) among the specimens. The strength deterioration factor of concrete containing GSBEA against sulphate attack was the lowest, with 1.31% at 90 days. The findings showed that ground SBEA could be used to enhance the sulphate attack resistance of concrete.

Leachate testing for delayed ettringite formation potential in cementitious systems

The aim of this research was to investigate the relation between leachate data and expansion due to delayed ettringite formation (DEF). These correlations have the potential for identifying the probability of delayed ettringite formation in a shorter time than the traditional method of monitoring expansion over time. Ions leached from the samples after heat curing of the cement paste were measured and the resultant data were used to calculate relative quasi-crystallization pressures within the cement microstructure. Potential relationships exist between these pressures, time to expansion initiation, and overall percent expansion of samples. The results indicate that sulfates and alkalis affect the onset and overall percent expansion observed. The calculated quasi-crystallization pressures strongly correlate with the observed overall percent expansion of mortar bars. Time to expansion initiation was negatively correlated with alkali content, indicating that cement with higher amounts of alkalis tends to expand at earlier ages. Overall, the leachate test corroborates earlier findings in the determination of DEF potential in cementitious materials and allows for the possible prediction of expansive behavior in 28 days or less using experimental results as opposed to cement composition.

Potential of Alkali-Silica Reactivity of Unexplored Local Aggregates as per ASTM C1260.

Alkali–silica reaction (ASR) is one of the major durability issues that affect the material degradation and structural performance, compromising the service life of concrete structures. Therefore, this study was planned to investigate the potential of ASR for locally available unexplored and vastly used aggregates, as per ASTM C1260. Aggregates from five different sources (Shalozan, Abbotabad, Orakzai, Swabi and Sada) were procured from their respective crusher sites. Mineralogical components of these aggregates were studied using the petrographic analysis. Cube, prism and mortar bar specimens were cast using mixture design in accordance with ASTM C1260 and placed in sodium hydroxide solution at 80 °C for 90 days. Identical specimens were also cured in water for the purpose of comparison. It was observed that mortar bar expansion of Orakzai aggregate was higher among the other tested aggregates and greater than 0.20% at 28 days, indicating the reactive nature according to ASTM C1260. Petrographic analysis also revealed the presence of reactive silica (quartzite) in the tested Orakzai source. It was observed that the compressive and flexural strengths of specimens exposed to ASR conducive environment was lower than the identical specimens placed in water. For instance, an approximately 9% decrease in compressive strength was observed for Orakzai aggregates exposed to ASR environment at 90 days compared to similar specimens placed in water curing. Moreover, microstructural analysis showed the development of micro-cracks for specimens incorporating Orakzai source aggregates. This study assists the construction stakeholders for the potential of unexplored local aggregates with regard to ASR before its utilization in mega construction projects.

Alkali−Silica Activity and Inhibition Measures of Concrete Aggregate in Northwest China

The alkali−silica reaction (ASR)-induced expansion of mortar bars containing four types of aggregates originating from different regions in northwest China was studied. The chemical composition, mineral composition, vitreous and amorphous substances, and expansion rates were determined using X-ray fluorescence, X-ray diffraction, polarizing microscope images, and the accelerated mortar bar test (AMBT). The inhibitory effects of fly ash and silica fume on the aggregate activity were evaluated. The binary mortar mixes were produced and tested, containing cement and fly ash or silica fume as the partial cement replacement. The microstructure and composition of the ASR products were analyzed by scanning electron microscope energy dispersive spectroscopy (SEM–EDS). The results show that all four types of aggregates exhibited an alkali activity, and that all expansion rates on the 14th day were higher than the standard of 0.1%. The lowest and highest values were 0.2% and 0.3%, respectively. The primary constituent in the chemical compositions of these aggregates was found to be silica. Polarization microscopy also confirmed that they contained alkali-active cryptolites. Fly ash and silica fume could both inhibit alkali activity expansion and the silica fume exhibited a superior inhibition effect. When the fly ash and silica fume contents were 20% and 10%, respectively, the expansion rates of the mortar bar on the 14th day were all less than 0.03%.

Mechanical, Swelling, and Thermal Properties of Geopolymer Mixture Containing Basic Oxygen Furnace Slag Aggregates

Basic oxygen furnace slag (BOFS) is a waste product generated during steel production. The utilization of BOFS in construction applications is considerably limited because of its inherent characteristics leading to volumetric expansion behavior caused by the chemical reaction between free lime (f-CaO) and water. The main objective of this paper is to investigate the material properties of normal mortar and geopolymer mixtures that contain BOFS aggregates. Three different aggregates were used to compare their performance, including siliceous river sand, fresh BOFS aggregate (within 1-month age), and stockpiled (more than 5-year age) BOFS aggregate. Test methods included a compressive strength test, accelerated mortar bar expansion test, and thermal conductivity test. Test results revealed that (1) geopolymer mixtures containing BOFS aggregate had comparable compressive strength with mortar mixture with river sand, (2) geopolymer mixtures have very low volume expansion, (3) thermal conductivity of geopolymer mixtures having both river sand and BOFS was lower than normal cement mortar mixture containing river sand. Therefore, geopolymer technology seems a key solution for converting BOFS slag into valuable construction materials. Therefore, a geopolymer mixture containing BOFS aggregate can be used as an energy-saving material.

Belitic calcium sulfoaluminate cement subjected to sulfate attack and sulfuric acid

Belitic calcium sulfoaluminate (BCSA) cement is a hydraulic rapid-setting cement with a different composition and properties compared to portland cement. There is currently limited information about its sulfate resistance and its resistance to sulfuric acid is not known. The ASTM C1012, Standard Test Method for Length Change of Hydraulic-Cement Mortars Exposed to a Sulfate Solution and a modified ASTM C1012 accelerated method were used to compare the sulfate resistance of BCSA cement, portland cement (PC), and PC-fly ash blends. BCSA cement, citric acid dosages in BCSA cement mixes, PC, and PC-fly ash blends were examined through mortar bar expansion. The most sulfate-resistant mixes contained BCSA cement or a blend of PC and class F fly ash. Citric acid dosage did not appear to affect resistance of BCSA cement to sulfate attack. Resistance of PC, PC-fly ash blends, and BCSA cement to a sulfuric acid solution was also compared. Compressive strength and volumetric changes were measured after prolonged immersion in sulfuric acid. Water to cementitious material (w/cm) ratios and curing time for BCSA were also analyzed to establish if these factors influenced resistance to sulfuric acid attack. The most acid resistant mix contained a blend of PC and class F fly ash. A higher w/cm (0.56) was found to be more resistant against sulfuric acid attack when using BCSA, while differing cure times did not clearly indicate sulfuric acid resistance.

Feasibility of sludge generated in water-based paint industries as cement replacement material

An estimated 2100 tonnes of solid sludge is generated per annum from the water-based paint industries of Bangladesh. This paint sludge (PS) is usually incinerated, consuming energy and generating greenhouse gases and other pollutants. Through chemical analysis and standardized tests, it was shown that PS contains a similar array of oxides as Ordinary Portland Cement (OPC) and has pozzolanic characteristics. Considering these, PS was examined as a cement replacement material to create an alternative and economically beneficial way of disposing of this waste. Cement paste and mortar samples were prepared by replacing 5%, 10%, 15%, 20% and 30% of OPC with PS. To assess mechanical and durability properties of PS-incorporated samples, different tests were carried out that included consistency, setting time, compressive strength, soundness, sulfate attack, alkali silicate reactivity and chloride diffusion. Both initial and final setting times of PS-incorporated cement increased with an increase in PS fraction but remained within the standard limit. Compressive strength increased for 5% PS replacement but decreased with further increase in PS replacement compared to 100% OPC mortar. A slightly higher rate of compressive strength gain was observed at later ages for PS-incorporated cement than 100% OPC, which confirmed the pozzolanic characteristic of PS. The addition of PS was found to reduce the expansion of mortar bars in both soundness and ASR tests. It also inhibited ettringite crystal formation in the mortar matrix for sulfate exposure. Initially, chloride permeability increased in the early days for PS-incorporated mortar but was found to decrease rapidly at later ages. Altogether, it may be concluded that a 15% replacement of OPC with PS would comply with the necessary strength and durability standards.

Mechanism understanding of alkali-silica reaction in alkali-activated materials system

To provide a better understanding of the mechanism of alkali-silica reaction (ASR) in alkali-activated materials (AAMs) system, in this work, the ASR behavior of alkali-activated slag (AAS)/fly ash (AAFA) mortars were investigated, and compared with ordinary Portland cement (OPC) mortars. It is found that although the AAS mortar bars experience the shrinkage first, the onset of ASR-induced expansion of AAS mortar bars is earlier than OPC mortar bars. In AAMs system, the reactive silica from aggregates is evidently dissolved and participated in the early-age alkali-activation, and thereby leads to the reduction of reactive silica for ASR. The Ca/Si ratio of amorphous ASR products in AAS mortars was lower, while Al/Si and Na/K ratios were higher than that of OPC mortars. Based on the obtained experimental evidences, a conceptual model was proposed to interpret and compare the ASR behavior in OPC, AAS and AAFA systems.

Dynamic elastic properties of hardened experimental mortar bars affected by accelerated alkali–silica reactivity test: a laboratory approach

The evaluation of ASR sensitivity of aggregates is of utmost importance due to durability and safety of structures and also due to economic reasons related to repairs or replacements of ASR-affected concrete. Laboratory tests for ASR detection rely mostly on petrographic examination and on laboratory expansion tests. The latter are mostly expressed in terms of length change (expansion) of experimental mortar bars subjected to the effect of alkaline environment. Along with this, recording of the propagating ultrasonic wave signal can increase reliability of test results. In the recent study, dynamic elastic properties of experimental mortar bars were recorded in both normal setting/hardening state (first 28 days) and in the conditions of accelerated ageing conditions in alkaline solution with elevated temperature (another 37 days). Setting/hardening of the studied materials under normal conditions was manifested by quasi-exponential P- and S-wave ultrasonic velocity increase. However, alkaline solution resulted in the rapid development of ASR phenomena in reactive aggregates and significant change of elastic wave velocities and other dynamic elastic parameters. Comparing various ultrasonic characteristics, dynamic ones (amplitudes, frequencies) proved significantly higher sensitivity and tighter correlation to length changes (expansion) cause by ASR than did the kinematic ones (elastic wave velocities, dynamic elastic moduli).

PROPERTIES OF CEMENT-FLY ASH MIXTURES WITH SUBSTANDARD FLY ASH AS A PARTIAL CEMENT AND FINE AGGREGATE REPLACEMENT

This research investigated the effects of using a substandard fly ash as a partial cement and/or fine aggregate replacement on the basic and durability properties of cement-fly mixtures. Experimental results showed that utilizing the substandard fly ash led to increase in water requirement and autoclave expansion of pastes. The strength activity indexes of the substandard fly ash passed the requirements of TIS 2135 and ASTM C618. Utilization of the substandard fly ash as cement replacement led to higher expansion of mortar bars stored in water and sodium sulfate expansion as compared to that of the OPC mixture. However, sodium sulfate resistance of mortar mixtures improved when utilizing the substandard fly ash as sand replacement material. The compressive strength of concrete at all ages was higher with the increase of the content of the substandard fly ash as sand replacement material. When the substandard fly ash was used as cement replacement material in concrete, the carbonation depth increased. On the other hand, the use of the substandard fly ash as sand replacement material decreased the carbonation depth of the concrete. Utilization of the substandard fly ash, both to replace cement and/or fine aggregate, reduced the rapid chloride penetration of the concrete.

Accelerated test for assessing the potential risk of alkali-silica reaction in concrete using an autoclave

To rapidly assess the potential risk of alkali-silica reaction (ASR) in concrete, an accelerated test using an autoclave by adopting multi-cycle 80 °C steam warming at atmospheric pressure is proposed. The influence of autoclave steam warming temperature, cycles/duration, and alkali dosage on expansion of mortar bars and concrete prisms was evaluated. Mechanical properties of concrete under accelerated ASR test were investigated. Furthermore, SEM-EDS analysis confirmed ASR products and indicated that the expansion is caused by ASR. The expansion limits considered for classifying aggregates were discussed. The experimental results demonstrated that the period required for assessing the potential risk of ASR in concrete (dacite aggregate in this study) can be shortened to 37 days.