Alkali Silica Gel Research Articles

Some amorphous materials are caused by weathering of concrete. - alkali-silica gel and non alkali-silica gel -

Some amorphous materials are caused by weathering of concrete. - alkali-silica gel and non alkali-silica gel -

Performance of ground clay brick in ASR-affected concrete: Effects on expansion, mechanical properties and ASR gel chemistry

The effects of ground clay brick (GCB) on alkali-silica reaction (ASR) expansion as well as on mechanical properties of ASR-affected concrete are investigated. Crushed red clay brick originated from demolished masonry was ground in a laboratory ball mill and replaced for portland cement at levels of 15% and 25% by weight in concrete mixes produced with alkali reactive sand. ASR expansion, compressive strength , flexural strength , and modulus of elasticity of the concrete mixes were evaluated. Effect of GCB on ASR gel chemistry was also studied on Pyrex glass-paste specimens using SEM/EDS (scanning electron microscope equipped with energy dispersive X-ray spectroscopy). The results indicate that GCB effectively reduces ASR expansion in concrete: associated cracking and loss on mechanical properties are also significantly reduced. SEM study suggests that GCB alters alkali silica gel chemistry thus resulting in a less expansive product.

알칼리 활성 고로슬래그 미분말 모르터의 알칼리-실리카 반응에 관한 실험적 연구

연구의 목적은 반응성 골재를 함유한 알칼리 활성화 고로슬래그 미분말의 알칼리-골재반응으로 인한 팽창을 조사하기 위한 것이다. 또한 이 연구는 현재 존재하고 있는 반응성 골재와 알칼리 재료들의 거동과 관련하여 특별히 관여 되어 지고 있다. 실험 방법은 EDS, SEM을 통하여 알칼리-실리카 반응 생성물의 구성이나 미세구조를 관찰하였으며 알칼리-실리카 반응에 의한 모르터 바의 팽창정도를 측정하였다. 실험 결과에 따르면 알칼리-활성화된 모르터는 알칼리 실리카 반응 때문에 팽창이 되었지만 14일 재령에서 0.1%의 팽창률을 나타내어 알칼리-실리카반응에 대하여 안전한 것으로 나타났다. 그리고 촉진 실험 후 SEM과 BEM분석한 결과 골재 주변과 시멘트 페이스트에 알칼리-실리카 겔 및 띠 모양의 생성물이 나타난 것을 볼 수 있었다. EDX에 따르면 반응생성물이 알칼리 활성화 고로슬래그를 사용하였을 경우 현격히 감소한 것을 볼 수 있다. 추가적으로 광물학적 혼화재료의 대체 재료로써 콘크리트 내구성의 특성을 보증하기 위하여 알칼리 활성화 고로슬래그의 품질을 향상시키는 연구가 필요하다. The purpose of this study was to investigate the expansion of alkali-activated mortar based on ground granulated blast furnace slag containing reactive aggregate due to alkali-silica reaction. In addition, this study was particularly concerned with the behavior of these alkaline materials in the presence of reactive aggregates. The experimental program included expansion measurement of the mortar bar specimens, as well as the determination of the morphology and composition of the alkali-silica reaction products by using scanning electron microscopy(SEM), and energy dispersive x-ray(EDX). The experiment showed that while alkali-activated ground granulated blast furnace slag mortars showed expansion due to the alkali-silica reaction, the expansion was 0.1% at Curing Day 14, showing that it is safe. After the accelerated test, SEM and BEM analysis showed the presence of alkali-silica gel and rim around the aggregate and cement paste. According to the EDX, the reaction products decreased markedly as alkali-activated ground granulated blast furnace slag was used. In addition, for the substitutive materials of mineral admixture, a further study on improving the quality of alkali-activated ground granulated blast furnace slag is needed to assure of the durability properties of concrete.

Macro- and micro-indicators of ASR in concrete pavement

Alkali–silica reaction produces deterioration of concrete, visible on the macro- and micro-scale. Macro-indicators of alkali–silica reaction are important in the field inspection of concrete. Micro-indicators help to verify the presence of alkali–silica reaction and make it easier to distinguish ASR from other degradation mechanisms. Three parameters were determined to evaluate the deterioration of concrete pavements: the specific length of cracks measured on the pavement surface; the specific length of cracks in the drill cores; and the volume of alkali–silica gels and microcracks in thin sections. According to these indicators, it was possible to distinguish two types of pavement degradation: degradation mainly associated by ASR and degradation connected with another mechanism. The macro- and micro-indicators linked the deterioration to alkali–silica reaction in six sites on the Czech highways. One site was attributed to another degradation mechanism. The rock types (and/or quartz recrystallisation of aggregates) affecting ASR were determined.

Alkali-silica reaction products: Comparison between samples from concrete structures and laboratory test specimens

Alkali-silica gels (ASG) were investigated in concrete from bridge structures (constructed from the 1920s to 2000), as well as in experimental specimens; employing optical microscopy, petrographic image analysis, and scanning electron microscopy combined with energy dispersive spectroscopy (SEM/EDS). The main differences were found in the chemical composition and morphology of the ASGs. ASGs which had formed in older concrete samples (50–80 years old) show a partly crystalline structure and higher Ca 2+ content, indicating their aging and maturation. Younger concrete samples and experimental test specimens exhibit the presence of amorphous ASG. The chemistry of ASG from experimental specimens reflects the chemical composition of accelerating solutions.

Comparative study of the alkali-silica reaction (ASR) in granitic aggregates

The reaction between certain reactive components of aggregates (like opal and metaestable silica) and concrete pore solution is well documented. Nevertheless, in this study it has been shown that some aggregates, like granite, could develop a rapid or slow alkali-silica reaction (ASR) depending on the deleterious component involved. Mortar bars were cast with two granitic aggregates extracted from concrete cores drilled in two Spanish Dams affected by ASR, being classified as granitic rocks. The main difference between them is the reactive component: microcrystalline quartz in one case and strained and microcracked quartz in the other case. A petrographic examination was carried out in the mortar bars. Thin sections were cut and the alkalisilica gel was stained for an easier detection. Then, the thin sections were examinated with a stereomicroscope comparing the differences in the progress of the ASR for both aggregates. It can be concluded that the main mechanism of formation and storage of gel is associated to the micro-cracks instead of the subgrain boundaries.

Effect of Silica Dissolution on the Mechanical Characteristics of Alkali-Reactive Aggregates

High pH nature of concrete microstructure can lead to chemical interaction between reactive silica in aggregate and alkali species in pore solution. As a result, alkali silica gel is rendered which can cause distress in hardened concrete. However, the consequence of silica dissolution is not only the gel formation and damage in cement paste, but also significant weakening of the reactive aggregate itself. In this study, three highly reactive, well-documented concrete aggregates were investigated. The aim was to characterize the micromechanical and -morphological alterations of the aggregates under aggressive alkaline solution by means of microscopy and nano-indentation techniques. It was found that silica dissolution alters micromorphology of the reactive aggregates and reduces elastic modulus and hardness values significantly.

Is alkali–carbonate reaction just a variant of alkali–silica reaction ACR = ASR?

The mechanism of the alkali–carbonate reaction (ACR) has been recognized as being different from that of the more common alkali–silica reaction (ASR). However, the identification of alkali–silica gel in ACR concrete from Cornwall, Ontario, Canada by Katayama, in 1992 raised the possibility that ASR was at least playing a role in the ACR reaction. The acid insoluble residues of the ACR aggregate from Kingston, along with two other aggregates were analyzed to determine what might be contributing to the reaction. The acid insoluble residue of the ACR Kingston rock contains 96% quartz of high solubility in NaOH. Good correlation was found between the amount of quartz and expansion of concrete prisms indicating that the expansion was due mainly to an alkali–silica reaction. This conclusion is supported by observations, in 2008, by Katayama of gel in thin sections of concrete made with the Kingston aggregate. It is concluded that ACR = ASR.

Mitigation of alkali–silica expansion in pulp fiber–mortar composites

Abstract The physical and microstructural effects of kraft pulp, thermomechanical pulp, and polypropylene fibers for restraining expansion due to alkali–silica reaction are investigated through expansion measurements, environmental scanning electron microscopy, and energy dispersive spectroscopy. This preliminary research revealed that thermomechanical pulp fibers are more effective at reducing expansion due to alkali–silica reaction than kraft pulp and polypropylene fibers. It is shown that the open lumen of the TMP fibers, and to some degree, the kraft pulp fibers, serves as a reservoir for alkali–silica gel, potentially minimizing internal expansive pressures. Furthermore, increases in the fiber volume fraction and fiber–cement bond strength (accomplished through extended initial moist curing) decreased expansion for all composites.

Composition of alkali–silica reaction products at different locations within concrete structures

Four concrete structures from Northern Portugal–three dams and one bridge–were studied. In the three dams concrete was produced with granitic aggregates. In the bridge, aggregates from an aluvial deposit were used. Pebbles show a wide range of lithologies, though dominantly siliceous. Petrographic techniques were applied in the study of these structures in which signs of deterioration were identified in order to confirm that the deterioration was caused by alkali–silica reactions. Alkali–silica gel was found in all the structures under different forms. It was verified that the texture and composition of the gel varies according to its location inside the concrete and also when compared with extruded gel. This finding is of interest in regard to the assumption that the composition of the gel is related to its expansivity. From the analyses carried out it was verified that silicon is always the main component. In some samples, calcium exists as the second most important component, but in others calcium is hardly detected. Alkalis show a low content in all the analyses. Sometimes aluminum is also detected. An attempt is made to correlate the composition of the gel to its location in concrete. The results are discussed in relation to data published by other authors.

Microstructural evolution of amorphous silica following alkali–silica reaction

Combining X-ray diffraction, NMR (CP-MAS and 29Si NMR-MAS) and diffuse reflectance infra-red Fourier transformed spectroscopy (DRIFTS), the local structural changes induced during the reactivity of amorphous (a-SiO2) under alkali–silica reaction (ASR) have been investigated. XRD patterns provide useful and new qualitative information concerning the reactivity of a-SiO2. A shift of the maximum of the halo towards the high values of 2θ is observed when the reaction progresses. NMR shows that ASR is accompanied in a-SiO2 by the diminution of Q4 species and by the formation of Q3 (and to a less extend to Q2) species. This importance played by Q3 species confirms the results obtained with natural alkali–silica gels. The formation of OH bonds observed by DRIFTS can be followed at ca. 950cm−1 and confirms NMR results. The microstructural state of silica (here represented by the medium- and short-range order (MRO) of amorphous silica) plays a crucial role in governing the kinetics of the ASR.

Petrographic identification of alkali–silica reactive aggregates in concrete from 20th century bridges

Cracks and white coatings have been observed in a number of concrete bridges constructed during the 20th century. The observed damage phenomena have been attributed to the alkali–silica reaction (ASR) after following detailed macroscopic examination. Several analytical approaches – optical microscopy of thin sections, petrographic image analysis and SEM/EDS study – were employed in order to: (1) quantify the extent of the damage (volume percentage of alkali–silica gel); (2) determine the causes of the damage. The presence of alkali–silica gels is controlled by the petrography of aggregates where monomineral quartz aggregates, metagreywacke, pellite and metasedimentary rock fragments contribute significantly to ASR development. Other phases (feldspars) and fragments of magmatic native rocks (granite, diorite, and volcanic rocks) have not been shown to have any influence on ASR. The volume of alkali–silica gels in the studied concrete samples (ranging from 0.1 to 0.9 vol.%) increases with increasing age of the bridge.

A Case Study of Concrete Pavement Deterioration by Alkali-Silica Reaction in Korea

The concrete pavement of the Seohae Highway in Korea has suffered from serious distress, only four to seven years after construction. Deterioration due to Alkali-Silica Reaction (ASR) has seldom been reported per se in Korea, because the aggregate used for the cement concrete has been considered safe against alkali-silica reaction so far. The purpose of this study is to examine the deterioration caused by an alkali-silica reaction of concrete pavement in Korea. The investigation methods included visual inspection and Automatic Road Analyzer (ARAN) analysis of surface cracks, coring for internal cracks, stereo microscopic analysis, scanning electronic microscope (SEM) analysis, and electron dispersive X-ray spectrometer (EDX) analysis. The results are presented as follows: the crack pattern of the concrete pavement in Korea was longitudinal cracking, map cracking or D-cracking. Local areas of damage were noticed four to five years after construction. The cracks started from edges or joints and spread out to slabs. The most intensive cracking was observed at the intersection of the transverse and longitudinal joints. Where cracking was the most intense, pieces of concrete and aggregate had spalled away from top surface and joint interface area. The progress of deterioration was very fast. The reaction product of alkali-silica gel was clearly identified by its generally colorless, white, or very pale yellow hue seen through a stereo optical microscopy. The typical locations of the reaction product were at the interface between aggregate and cement paste in a shape of a rim, within aggregate particles in the cracks, and in the large void in the cement paste. Most of the white products were found at interface or internal aggregates. SEM and EDX analysis confirmed that the white gel was a typical reaction product of ASR. The ASR gel in Korea mainly consisted of Silicate (Si) and Potassium (K) from the cement. The crack in the concrete pavement was caused by ASR. It seems that Korea is no longer safe from alkali-silica reaction.

The determination of gel swelling pressure of reactive aggregates by ASGPM device and a new reactive-innocuous aggregate decision chart

Alkali-silica reaction occurs when reactive silica in aggregates chemically reacts with alkaline components of cement, forming alkali-silica gel that has harmful effects on concrete because of high swelling capacity and internal pressure. In this study, alkali-silica gel pressure measuring (ASGPM) tests were carried out on specimens comprising opal, chert, chalcedony, andesite, greywacke, basalt, ignimbrite, granodiorite and quartzite aggregates obtained from field or open quarries of Turkey for examination of effects of reactive aggregate types on pressure measurements. The highest alkali-silica gel pressure was measured on cylindrical mortar that included opal (2.81 MPa), the lowest on mortar containing quartzite (0.26 MPa). The rate of alkali-silica gel pressure development was calculated by dividing the pressure values by duration of the experiment. By using these rate values, a new deleterious–innocuous aggregate decision chart was suggested. Furthermore, this decision chart’s classification was compared with ASTM C 289 chemical method, ASTM C 227 mortar bar test, and ASTM C 1260 accelerated mortar bar test method.

Examination of the concrete from an old Portuguese dam: Texture and composition of alkali–silica gel

Exudations and pop-outs were identified in the interior galleries of a large dam built in the 1960s. The samples collected were examined by a Scanning Electron Microscope. A dense material with a smooth surface and drying shrinkage cracks or a spongy texture were observed in the samples. The semi-quantitative composition was obtained by energy dispersive spectrometry (EDS) and it was concluded that this material corresponds to alkali–silica gel, composed of SiO 2–Na 2O–K 2O–CaO. A viscous white product in contact with an aggregate particle in a cone sampled from a pop-out was observed through use of the scanning electron microscope and it has characteristics similar to the gel present in the exudations and cavities. Reference is made to the potential alkali reactivity of the aggregate present in the concrete. The texture and composition of the products probably resulting from an alkali–silica reaction are presented, set out in ternary diagrams, and discussed.

Influence of matrix properties on alkali silica reaction rates

Matrices with different cracking and confinement characteristics are utilized to isolate the important parameters that influence gel initiation and alkali silica reaction rate. The paper is divided into two parts. In Part I, the matrix exhibits crack growth resistance behavior which induces compressive stresses on the alkali silica gel and in addition prevents the alkali silica gel from leaving the reaction site, which slows down the alkali silica reaction rate and modifies the gel composition. In Part II the matrices are designed to provide little confinement and hence allow the alkali silica gel to expand almost freely. However, the matrices in Part II differ in their ability to allow the alkali silica gel to escape the reaction site. The results reveal that lack of confinement accelerates early gel formation whereas the lack of escape of alkali silica gel products away from the reaction site reduces the alkali silica reaction rate.

Investigation of mixing ratio and restraint condition effects on alkali–silica gel pressure in mortar by using a uniaxial alkali–silica gel pressure measuring device (ASGPM-D)

A pressure of alkali silica gel which is the product of alkali–silica reaction causes pattern crack development and ultimately failure in cement based materials. This paper examines the measurement of alkali–silica gel pressure in cylindrical mortar specimen by a new test device (alkali–silica gel pressure measuring device, ASGPM-D) and investigates also the effects of the test medium on test results. Specimens of various sizes and geometries were tested to develop standard specimen size for ASGPM test method. The most suitable specimen with diameter of 35 mm and 250 mm in length was selected by optimizing the experimental results. Furthermore, the highest alkali–silica pressure value was recorded on a specimen which has 0.45 w/c and 74–150 μm grain size in an 80 °C 1 N NaOH solution. Also, swelling pressures of four reactive aggregates (opal, chert, basalt and chalcedony) were determined under two distinct restraint stages (1.5 kN and 3 kN).

Crystallized alkali-silica gel in concrete from the late 1890s

The Elon Farnsworth Battery, a concrete structure completed in 1898, is in an advanced state of disrepair. To investigate the potential for rehabilitation, cores were extracted from the battery. Petrographic examination revealed abundant deposits of alkali silica reaction products in cracks associated with the quartz rich metasedimentary coarse aggregate. The products of the alkali silica reaction are variable in composition and morphology, including both amorphous and crystalline phases. The crystalline alkali silica reaction products are characterized by quantitative X-ray energy dispersive spectrometry (EDX) and X-ray diffraction (XRD). The broad extent of the reactivity is likely due to elevated alkali levels in the cements used.

The microstructure of concrete made with municipal waste incinerator bottom ash as an aggregate component

The interaction of municipal solid waste incinerator bottom ash (MSWI bottom ash), when utilized as an aggregate in concrete, with the cement matrix was investigated. The most prominent reaction observed in lab and field concrete was the formation of aluminium hydroxide and the release of hydrogen gas from aluminium grains reacting in the alkaline environment. The expansive aluminium reaction was identified as a main cause of extensive spalling on the concrete surface. Due to the higher content of bottle glass as part of the ash, in all samples, reaction products of an alkali-silica reaction (ASR) could be observed as well. However, damage due to ASR were less severe than those caused by the aluminium reaction. The expansion rates were low and only a few of the lab samples showed cracking. Microstructural analysis of the samples indicated clearly that a large quantity of the alkali-silica gel which was formed was accommodated in the pores and voids without exerting any strain on the material.

AAR-5: Rapid preliminary screening test for carbonate aggregates

The ultra-accelerated mortar-bar test (AAR-2) has been widely and successfully used as a screening test to identify aggregates that are potentially alkali-reactive. However, there are exceptions; some aggregates that, though alkali-reactive according to both field experience and concrete prism test results, do not show as such in the mortar-bar test. Trials carried out by members of RILEM TC 191-ARP have established that these aggregates include carbonate materials. It has been found that any potential reactivity of such carbonate aggregates will be identified if 4/8 mm aggregate is used for making the bars instead of 0/4 mm aggregate. The development of this method (AAR-5), which is sometimes termed the ‘concrete microbar’ test, and the international trials organised by RILEM TC 191-ARP are described in [1]. The concrete microbar method is particularly beneficial when the aggregate contains both reactive silica and a kind of dolomite that is prone to dedolomitization. In the mortarbar test most of the (fine) aggregate will dedolomitize throughout, whilst in the concrete microbars only the outer shells of the (coarser) aggregate is dedolomitized [2]. This difference seems to explain why, though alkali-silica gel develops in both the tests, the aggregate develops more pressure and expansion in AAR-5 than in AAR-2. It is therefore recommended that, if dolomitic carbonate aggregates are being assessed, both the AAR-2 and the AAR-5 tests should be carried out. If the concrete microbars expand The text presented hereunder is a general draft for general consideration. Comments should be sent to the TC Chairman Dr. Philip J. Nixon, Building Research Establishment, Garston WD2 7JR Watford, United Kingdom; Tel: +44 923 664 239; Fax: +44 923 664 786; Email: nixonp@bre.co.uk, by 30 April 2006.