Alkali-carbonate Reaction Research Articles

Inhibition of the Alkali-Carbonate Reaction Using Fly Ash and the Underlying Mechanism

In this paper, fly ash is used to inhibit the alkali-carbonate reaction (ACR). The experimental results suggest that when the alkali equivalent (equivalent Na2Oeq) of the cement is 1.0%, the adding of 30% fly ash can significantly inhibit the expansion in low-reactivity aggregates. For moderately reactive aggregates, the expansion rate can also be reduced by adding 30% of fly ash. According to a polarizing microscope analysis, the cracks are expansion cracks mainly due to the ACR. The main mechanisms of fly ash inhibiting the ACR are that it refines the pore structure of the cement paste, and that the alkali migration rate in the curing solution to the interior of the concrete microbars is reduced. As the content of fly ash increases, the concentrations of K+ and Na+ and the pH value in the pore solution gradually decrease. This makes the ACR in the rocks slower, such that the cracks are reduced, and the expansion due to the ACR is inhibited.

Alkali-dolomite reaction in air lime mortar – implications for increased strength and water resistance

Abstract This paper investigates the origin of increased strength and water resistance of air lime mortar prepared by Triassic dolomite aggregate when exposed to humid or wet environments. The mortar specimens were exposed to various ageing conditions and analysed using petrographic and scanning electron microscopy equipped with X-ray microanalysis. Parallel to these analyses, X-ray powder diffraction and strength tests were performed on the specimens. It was revealed that reactions associated with the dedolomitisation process of the dolomite grains in the lime binder (hereafter alkali-carbonate reactions or ACRs) are the source of the improved strength and water resistance. An increasingly alkaline environment accelerated the ACRs substantially. Two parallel processes during the ACRs (dedolomitisation and CaCO3 dissolution/reprecipitation) were described in detail. Ageing temperature decisively influenced the kinetics of the dedolomitisation and dictated the path of the CaCO3 dissolution/reprecipitation process. After two years of ageing in a water-saturated environment at 60 °C, air lime mortar retained a great deal of its initial mechanical strength, and at 20 °C its strength was considerably increased. This somewhat unexpected observation was explained as being a result of microstructural changes and/or phase transitions.

Expansion of Dolomitic Rocks in TMAH and NaOH Solutions and Its Root Causes.

In this paper, a tetramethylammonium hydroxide (TMAH) solution and homemade cement without alkali were used to eliminate the influence of the alkali-silica reaction (ASR) on the expansion of dolomitic rocks, and a NaOH solution was used as a comparison agent. The expansion of concrete microbars and dolomite powder compacts prepared from dolomitic rocks was tested. The expansion cracks and reaction products were investigated by X-ray diffraction, optical microscopy, scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The results showed that TMAH reacts with dolomite crystals in dolomitic rocks to form brucite and calcite. Through X-ray diffraction and SEM-EDS analysis, it can be determined that the chemical reaction between TMAH and dolomite crystal was dedolomitization. The expansion stress test and concrete microbar expansion test suggest that the alkali carbonate reaction (ACR) can produce expansion. Although both the ASR and the ACR were observed in the NaOH reaction system, but ASRgel was not found in the cracks, indicating that the ASR may be involved in the expansion process of concrete microbars and that the ACR is the root cause of the expansion. However, under the curing conditions of the TMAH solution, many ACR products were found around the crack, indicating that the expansion of the concrete in this system was caused entirely by the ACR.

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.

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.

Spremembe mikrostrukture cementne malte zaradi alkalno-karbonatne reakcije

Spremembe mikrostrukture cementne malte zaradi alkalno-karbonatne reakcije

Physical characterization and alkali carbonate reactivity (ACR) potential of the rocks from Bauhti Pind and Bajar area Hassan Abdal, Pakistan

This study is conducted to evaluate aggregate characteristics and alkali carbonate reactivity (ACR) potential of carbonate rocks of the Bouhti Pind and Bajar area, Hassan Abdal, Pakistan. Physical and chemical tests were performed to assess aggregate suitability. Mean specific gravity (2.65–2.65), water absorption (0.51–0.68%), Los Angeles abrasion (24.78–26.10%) and sulphate soundness values (2.86–4.25%) of the carbonate rocks of these areas are within specified limits of their respective standards. Petrographic studies of Bajar area reveal the presence of 96.3% calcite, 2% clays, 1% hematite and 0.7% quartz. These rocks do not contain dolomite and show no expansion in rock cylinder test. Therefore, the aggregate is not prone to ACR and can be used in cement concrete. Rocks of Bouhti Pind area have mean 92% calcite, 3.8% dolomite, 2% clays, 1.2% hematite and 1% monocrystalline quartz. The amount of deleterious minerals specifically dolomite and clays are below the maximum allowed limit to initiate ACR. However, one of the rock cylinders shows 0.043% expansion which is below threshold limit of 0.10% to cause ACR as specified in ASTM C-585. Hence, these carbonate rocks qualify physical characterization and ACR tests and can be used in the construction of roads and in cement concrete.

Detailed investigation of ACR in concrete with silica-free dolomite aggregate

Abstract The progress of the alkali-carbonate reaction (ACR) in NaOH or an aqueous environment at elevated temperature (60 °C) was investigated in concrete prepared with silica-free dolomite aggregate. The results obtained show that chemical reactions characteristic for the ACR progressed in all aged concrete systems. In NaOH aged samples, dolomite grains smaller than 2 mm in diameter went through a complete dedolomitisation process. Additionally, new Mg-Al, Mg-Si and Mg-Al-Si phases were recognized at the aggregate-cement paste interface. The less alkaline environment in the case of H2O-aged samples resulted in substantially decelerated ACR reaction. Based on observed long-term microstructural and phase changes, a detailed scheme of the ACR in concretes with silica-free dolomite aggregates was proposed. It turned out that the soluble Si-source does not necessarily originate from the aggregate itself but rather through the Pozzolanic reaction of cement binder decomposition/regeneration cycle.

The Expansion Cracks of Dolomitic Aggregates Cured in TMAH Solution Caused by Alkali⁻Carbonate Reaction.

In this study, concrete microbars and rock prisms made of dolomitic aggregates were cured in a 1-mol/L tetramethylammonium hydroxide (TMAH) solution at 80 °C to avoid the effect of alkali–silica reaction (ASR) on expansion. The expansion of specimens was only caused by the alkali–carbonate reaction (ACR). The reason that self-made cement was used in this work was to ensure that the Mg2+ contained in the brucite originated only from dolomite. Expansion of concrete microbars and rock prisms was measured, the expansion cracks were systematically observed by orthogonal polarizing microscopy, and the products of ACR were analyzed by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The results showed that the dolomite crystals in the dolomitic aggregates reacted with the TMAH solution and resulted in ACR, which formed calcite and brucite and led to cracking of the specimens. The source of the expansion was the dolomite crystals of the dolomite enrichment area. Expansion cracks either extended inside the rock or into the cement phase and eventually disappeared. The alkali–carbonate reaction significantly contributed to the expansion of dolomitic aggregates cured in TMAH solution at a later curing age.

Effects of curing condition and particle size of aggregate on the expansion and microstructure of dolomitic aggregates cured in TMAH solution.

In this paper, the modified microbars prepared by dolomitic aggregates with three kinds of particle size and self-made cement without K+ and Na+ were cured in 1 and 2 N tetramethyl ammonium hydroxide (TMAH) solution at 20°C, 60°C and 80°C, respectively. TMAH was used as curing solution to exclude the expansion contribution of alkali–silica reaction. Effects of the concentration of TMAH solution, curing temperature and aggregate grain size on the expansion of dolomitic aggregates were systematically investigated to determine the expansion characteristics only caused by alkali–carbonate reaction (ACR). Expansion of modified microbars cured in TMAH solution was measured. The porosities of original and reacted aggregates were also measured. Microstructural studies were carried out by scanning electron microscopy (SEM) and thermo-gravimetric (TG) analysis. The results showed that the aggregate grain size and curing temperature can influence the expansion of modified microbars significantly. When the modified microbars prepared by aggregates with 2.5–5 mm grain size and cured in 1 N TMAH solution at 80°C, the samples exhibited obvious expansion only caused by ACR, which is beneficial to detect the ACR reactivity of dolomitic rocks exclusively in concrete engineering. Based on the pore structure analysis, there was a slight increase (13%) in porosities of aggregates cured for 140 days at 80°C. Rod-like brucite crystals formed in the process of ACR were also found in TG analysis and SEM images.

Chemical corrosion of external stairs – case study

On the basis of examinations of the efflorescences formed on the concrete surface, an attempt was made to analyze the sources of concrete corrosion without entering inside the construction. The concrete stairs revealed the symptoms of leaching, as a result of alkali-aggregate reactions developing beneath the surface. As a result of this corrosion process and the carbonation propagating from the concrete surface, the carbonate efflorescences were found. Their phase composition was determined by X-ray diffraction. In order to identify whether the efflorescences were the results of the alkali-silica reaction or alkalicarbonate reaction, the microstructure was investigated using the scanning electron microscope together with energy dispersive spectroscopy.

Assessment of the Alteration of Granitic Rocks and its Influence on Alkalis Release

Several concrete structures had shown signs of degradation some years after construction due to internal expansive reactions. Among these reactions there are the alkali-aggregate reactions (AAR) that occur between the aggregates and the concrete interstitial fluids which can be divided in two types: the alkali-silica reaction (ASR) and alkali-carbonate reaction (ACR). The more common is the ASR which occurs when certain types of reactive silica are present in the aggregates. In consequence, an expansive alkali-silica gel is formed leading to the concrete cracking and degradation. Granites are rocks composed essentially of quartz, micas and feldspars, the latter being the minerals which contain more alkalis in their structure and thus, able to release them in conditions of high alkalinity. Although these aggregates are of slow reaction, some structures where they were applied show evidence of deterioration due to ASR some years or decades after the construction. In the present work, the possible contribution of granitic aggregates to the interstitial fluids of concrete by alkalis release was studied by performing chemical attack with NaOH and KOH solutions. Due to the heterogeneity of the quarries in what concerns the degree of alteration and/or fracturing, rock samples with different alteration were analysed. The alteration degree was characterized both under optical microscope and image analysis and compared with the results obtained from the chemical tests. It was concluded that natural alteration reduces dramatically the releasable alkalis available in the rocks.

Long-Term Effects of Different Cementing Blends on Alkali-Carbonate Reaction

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The effect of trass and fly ash in minimizing alkali-carbonate reaction in concrete

The influence of natural pozzolans on the controlling of the alkali-carbonate reaction (ACR) and the alkali-silica reaction (ASR) has not been studied comprehensively, regardless of the research studies conducted on utilizing natural pozzolans as supplementary cementitious materials. Nevertheless, the performance of natural pozzolans toward the ACR and ASR was investigated in recent studies. The primary purpose of this research is to evaluate the alkali-carbonate expansion of mortar specimens, which contain trass and fly ash in the short-term. For the short-term, the extent of expansion due to ACR was monitored for fourteen 7-day intervals. Based on the test result, fly ash and trass meaningfully reduced the expansion due to ACR in the short-term. Moreover, long-term test results for trass were presented as well. For the long-term, samples were kept at 80°C in NaOH solution for curing in 56days according to ASTM C1260 and 390days according to ASTM C1293. The observations by optical microscopy have been conducted on thin sections.

Environmental controls and reaction pathways of coupled de-dolomitization and thaumasite formation

Deteriorated concrete and interstitial solutions (IS) were collected from Austrian tunnels to elucidate potential connections between de-dolomitization caused by coupled alkali carbonate reactions (ACR) and thaumasite form of sulfate attack (TSA). A conceptual reaction model for the portlandite–CSH phases–dolomite–calcium sulfate–calcite–brucite–thaumasite system was developed based on experimental data, hydrochemical modelling, IS chemistry and apparent concrete compositions. During the initial stage of sulfate attack, ettringite and gypsum formation weakened the concrete's microstructure and initiated ACR. Leaching of hydrated cement phases resulted in IS with a pH ~ 12-13, which promoted incongruent dolomite dissolution. Infiltration of Ca–SO4–type ground water into the de-dolomitization zone facilitated calcite and brucite neo-formations at 13>pH>10.5 during advanced states of concrete deterioration and subsequently resulted in thaumasite precipitation at pH~8.7. In this contribution, the reaction mechanisms and environmental controls of de-dolomitization are discussed in relation to the durability of concrete under sulfate attack.

The enigma of the ‘so-called’ alkali–carbonate reaction

The so-called alkali–carbonate reaction (ACR) consists of two distinct reactions: the non-expansive dedolomitisation reaction and deleteriously expansive alkali–silica reaction of cryptocrystalline quartz hidden in the dolomitic limestone aggregate. In the past, dedolomitisation was confused with ACR and regarded as associated with the expansion mechanism, whereas alkali–silica gel was not observed using conventional optical microscopy. This led to a long-standing controversy, but the enigma has been resolved by careful petrographic examination of typical ACR concretes made with the type aggregate from the Pittsburg quarry, Ontario, including an experimental sidewalk in Kingston. This paper introduces the historical background of this issue and the essence of recent studies from the petrographic viewpoint by the authors who actually examined the typical ACR in Ontario.

Types of alkali–aggregate reactions and the products formed

The alkali–aggregate reaction comprises the alkali–silica reaction (ASR) and the alkali–carbonate reaction (ACR). Reaction kinetics of the ASR depends on the grain size and crystalline structure of the reactive silicon dioxide. The reaction starts in the aggregates along the particle periphery and progresses inward. After cracking of the particle, larger amounts of reaction products are formed and are eventually extruded in the cement paste, where they fill cracks and voids. ASR products within aggregates predominantly consist of (hydrated) silicon, alkalis and calcium with characteristic atomic ratios of (Na + K)/Si ∼ 0·25 and Ca/Si ∼ 0·25. They take up additional calcium while releasing alkalis when extruded. Amorphous and crystalline reaction products occur and coexist. Expansion is the result of water adsorption by the reaction products. In ACR, harmless dedolomitisation is distinguished from deleterious reaction of fine-grained silica disseminated throughout the carbonate matrix. Further research is needed to gain more in-depth knowledge about the thermodynamics and kinetics of ASR products and the mechanisms of expansion. This should allow the establishment of a better link between concrete structures and both accelerated testing and models.

Experimental investigations to evaluate the alkali-carbonate reactivity and alkali-silica reactivity of aggregates

The objective of this paper was to evaluate the alkali-silica reactivity (ASR) and alkali-carbonate reactivity (ACR) of the 14 aggregate groups quarried from different locations. In order to serve the stated purpose, the investigated aggregate groups were tested in determining their alkali-silica reactivity using the ASTM C 1260 at the ages of 2, 4, and 8 weeks, and the modified ASTM C 1293 (prisms submerged in the 1N NaOH at 80°C) at the test durations of 4, 8 and 13 weeks. The aggregate prone to the alkali-carbonate reactivity was accessed using the ASTM C 1105 at the ages of 3, 6 and 12 months. The study revealed that the aggregates susceptible to alkali-carbonate reactivity were also shown to be reactive due to the alkali-silica reactivity.

Influence of alkali carbonate reaction on compressive strength of mortars with air lime binder

This paper investigates the process of alkali-carbonate reaction (ACR) in air lime mortar prepared with Triassic dolomite aggregate. The progress of the ACR at various exposure conditions, i.e. accelerated conditions of 1M NaOH at 60°C, distilled water at 60°C, and 1M NaOH solution at 20°C, and reference conditions (water at 20°C) was studied using petrographic microscope and scanning electron microscopy with X-ray microanalysis (SEM/EDS). As a control, an air lime mortar with inert limestone aggregate was prepared and submitted to the same conditions. Parallel and complementary to the microscopic investigation, the compressive strength, weight and length of the mortar bars was measured over the exposure time. The results of the tests indicate that the presence of hydroxide ions in the binder is sufficient to trigger and promote the ACR in the lime mortar with dolomite aggregate. More alkaline conditions brought about by alkali hydroxides and the higher temperature of 60°C accelerate the reaction. Compressive strength of the lime mortar with dolomite aggregate, exposed to water or the NaOH solution, increased with time considerably, as a consequence of the progressing ACR.

Utilizing Asphaltic Concrete Overlay to Mitigate the Detrimental Effects of Alkali Carbonate Reactions in Portland cement Concrete Pavement

In 1990, the Louisiana Department of Transportation and Development (LADOTD) constructed approximately 9.96 km of portland cement concrete (PCC) pavement on Interstate 20. In 1994, the PCC began to show signs of distress in the form of surface cracks, joint spalling, pop outs, and efflorescence. Alkali carbonate reactions (ACR) in the PCC were discovered upon analyzing cores taken from the PCC in 1996. In 1997 and 1998, LADOTD placed a 102-mm AC overlay on the PCC pavement on the east- and west-bound lanes, respectively. Sawing and sealing the AC over the PCC joints was performed to mitigate reflective cracking. The AC overlay added structure to the pavement section reducing stress on the PCC, created a barrier preventing surface moisture from entering into the PCC, and created a thermally insulated pavement reducing the temperature within the PCC. Pavement surface distress data was obtained by data mining the LADOTD Pavement Management system data base and structural testing the composite pavement was conducted with the Falling Weight Deflectometer. Cores were obtained from the PCC and tested in accordance with a modified ASTM C1567-13 in October 2012. Approximately 15 years after the placement of the AC overlay, only minimal transverse cracking, longitudinal cracking, and patching were discovered and the roadway had a smooth ride. Results from the structural testing indicated that the PCC pavement was distressed with the overall structural number of the pavement being approximately 5.5. When tested in accordance with a modified ASTM C1567-13, significant volumetric strains up to 0.8 percent were measured on the PCC cores. Volumetric strains of that magnitude will cause detrimental effects on the PCC, eventually leading to its destruction.