Mortar Expansion Research Articles

Monitoring Concrete Deterioration Due to Reinforcement Corrosion by Integrating Acoustic Emission and FBG Strain Measurements.

Corrosion of concrete reinforcement members has been recognized as a predominant structural deterioration mechanism for steel reinforced concrete structures. Many corrosion detection techniques have been developed for reinforced concrete structures, but a dependable one is more than desired. Acoustic emission technique and fiber optic sensing have emerged as new tools in the field of structural health monitoring. In this paper, we present the results of an experimental investigation on corrosion monitoring of a steel reinforced mortar block through combined acoustic emission and fiber Bragg grating strain measurement. Constant current was applied to the mortar block in order to induce accelerated corrosion. The monitoring process has two aspects: corrosion initiation and crack propagation. Propagation of cracks can be captured through corresponding acoustic emission whereas the mortar expansion due to the generation of corrosion products will be monitored by fiber Bragg grating strain sensors. The results demonstrate that the acoustic emission sources comes from three different types, namely, evolution of hydrogen bubbles, generation of corrosion products and crack propagation. Their corresponding properties are also discussed. The results also show a good correlation between acoustic emission activity and expansive strain measured on the specimen surface.

Risk of ASR in coating mortars incorporating glass aggregates and a Portland–limestone cement

As the cement content is one of the parameters that control alkali–silica reaction (ASR), this study examined its influence on the expansion of glass mortars. The mortars had volumetric ratio of 1:4 (cement: aggregate) and various aggregate compositions, obtained using replacement ratios of natural sand with waste glass, of 0, 20, 50 and 100%. A volumetric ratio 1:4 was chosen because it is a current composition for cementitious coating mortars. In fact, mortar mixes with increased cement content can lead to erroneous conclusions for in situ mixtures with reactive aggregates. It is concluded that it is feasible to produce glass mortars without deleterious ASR expansion depending on the amount of cement used. For normal cement/aggregate ratios for coating mortars (1:4, in volume), a CEM II/B-L 32.5 N mortar with glass incorporation has a low ASR risk.

Research on Performance of CRTS I Cement-Emulsified Asphalt Mortar on Site

For construction method of infusion bag, expansion of CRTSⅠCA mortar on site by core drilling, water absorption, chloride ion permeability and frost resistance and other properties were studied in comparison with performance of mortar in laboratory under standard curing. The results showed that expansion of the mortar on site was 2%, water absorption was 0.5%, charge amount was 210C, quality loss after 300 freeze-thaw cycles was -1.1%, the performance was much better than molded mortar in laboratory. Pore structure analysis showed that the internal pore diameter of the mortar on site was about 150μm, pore content was 9% to 12%; the internal pore diameter of the mortar in laboratory was also about 150μm, pore content was 10% to 15%. China railway track system（CRTSⅠ）slab ballastless track is one of the main structure forms of the modern high-speed railway and mainly composed of concrete basement, the Cement-emulsified Asphalt Mortar layer and concrete slab, featured by its rapid construction, convenient maintenance, and so on, has been widely applied in high-speed railway construction in our country. The cement-emulsified asphalt（CA） Mortar is one of the key materials and structures in slab ballastless track, providing the appropriate stiffness and elasticity which is usually composed of cement, emulsified asphalt, grit, water and many types of additives, containing a variety of inorganic/organic compositions and many types of surfactants, through the special bag, filling inside the flat cavity by its own weight between track slab and concrete basement with a thickness of 50mm (length×width 4962 mm×2400 mm). The construction method of CA mortar is grouting the non-woven fabrics bag after setting the bag under the track slab fixed by fine adjustment claw, which is convenient and has no requirement of mould removal. The bag is fixed before the perfusion process and does not produce wrinkles. The method greatly enhances the construction efficiency and has been widely utilized in high-speed railway. To full perfusion and tightness with track board, CA mortar contains gas former and expands after the end of infusion in a restricted state. Non-woven fabrics bag itself with breathable permeable, a small amount of water seeps around infusion bags in a period of time after the end of the infusion. Theoretically free water seepage of mortar on the one hand increases the compactness and durability of the mortar, but on the other hand will reduce the mortar expansion; the quality of filling layer mortar can meet the acceptance requirements in the engineering practice. In the same raw materials and mortar mixing, the performance of fresh mortar can require CRTSⅠ type of slab track emulsified asphalt cement mortar in high-speed railway Q / CR 469-2015. After water seepage performance of hardening mortar on site is different from laboratory mortar, because the surface of laboratory mortar is without compression and free deformation. In this paper, contrast mortar on site and molded mortar in laboratory, the performance of hardened mortar on site were studied.

Application of ASR tests to recycled concrete aggregates: Influence of water absorption

Concrete is one of the most abundant construction and demolition wastes. It can be crushed to produce Recycled Concrete Aggregates (RCA) that can eventually be recycled for the manufacture of new concrete. However, the presence of adherent cement paste leads to higher alkalis content in these aggregates that could increase the risk to observe Alkali Silica Reaction (ASR). Moreover, the origin of natural aggregates in the RCA is generally unknown and these aggregates can potentially be reactive concerning ASR. Among standards which qualify the risk of ASR for natural aggregates, two main tests are used in this paper to evaluate the risk of ASR of RCA: tests on mortars and tests on microbars. In these tests, the water absorption of aggregates is not taken into consideration for the effective water calculation. However, in the case of absorbing aggregates like RCA, absorption water cannot be neglected. It could change significantly the effective water to cement ratio, and then influence the measured expansion. The first aim of this paper is to study the influences of absorption water and initial saturation state of RCA on the expansion of mortars and microbars. The second objective is to propose a new simple method for the assessment of water absorption coefficient of the fine granular fraction 0.16/0.63mm used for the manufacture of microbars. It is shown that absorption water has a strong influence on the expansion of mortars and microbars made with RCA, and that it has to be taken into account in the composition of the mixes. The initial state of saturation of RCA is less influential. The proposed method for the water absorption coefficient determination of fraction 0.16/0.63mm is based on the correlation between water absorption and cement paste content. The estimation of the latter from the mass loss between 105 and 475°C for two fractions of RCA, allows for an accurate determination of the water absorption coefficient of the fine fraction.

Study of effect of electric arc furnace slag on expansion of mortars subjected to alkali-aggregate reaction

Abstract Alkali-aggregate reaction is a chemical reaction between cement alkalis and some reactive mineral present in some aggregates, leading to concrete expansion and cracking. One kind usually observed and studied in Brazil is the alkali-silica reaction, due to its fast development. There are several methods that are effective to control and mitigate this reaction, and one of them is the partial replacement of cement by mineral additions such as pozzolans like fly-ash, silica fume and slag. In this study, we propose the use of electrical steel slag as a partial replacement of cement, evaluating its effectiveness by NBR 15577:2008, employing different proportions as replacement. It seems that the electrical steel slag, despite its expansive behavior, has been effective in the control of the ASR.

2성분계 지오폴리머 모르타르의 알칼리-실리카 반응에 관한 연구

The purpose of this study is to investigate the alkali-silica reaction through the addition of reactive aggregate in the alkali-activated geopolymer mortar. This study also carried out to analyse the behavior of these alkaline materials in the presence of reactive aggregate. The test method included mortar-bar method to measure the rate of expansion of the mortar bar specimens and morphological analysis and determining composition of the alkali-silica reaction products by using scanning electron microscopy (SEM) and energy dispersive x-ray (EDX). As a result, it was shown that the rate of expansion of the alkali-activated geopolymer mortars changed. At day 14, geopolymer mortar appeared to be safe with less than 0.1%. After the accelerated test, SEM 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, the study on improving the quality of alkali-activated mortar bar by substituting other materials of mineral admixture is needed to assure of the durability properties of concrete.

Experimental study and empirical modeling of lithium nitrate for alkali-silica reactivity

The influence of various dosages of lithium nitrate salt to inhibit the ASR-induced expansions of six reactive aggregates was studied. ASTM C 1260 (commonly known as Accelerated Mortar Bar Test (AMBT)), and modified AMBT were used to measure linear expansions of control mortar bars containing no lithium content and those of the mortar bars treated with up to six dosages of lithium-to-alkali molar ratios of 0.59, 0.74, 0.89, 1.04, 1.19 and 1.33, respectively. An empirical model to predict the minimums dosages of lithium salt required to suppress the excess mortar expansion below the prescribed failure limits at 14, 28 and 56days was developed. The study revealed that a good correlation existed between the optimum lithium content obtained by the experimental procedures and that evaluated by the proposed model. It was also found that the amount of lithium nitrate salt needed to suppress ASR-induced mortar expansion varied depending upon the extent of aggregate reactivity, the mineralogy of the aggregates, and the test duration.

The role of lithium compounds in mitigating alkali-gravel aggregate reaction

Alkali reaction with reactive aggregates is an example of concrete internal corrosion. Cracks and damage to elements of a concrete structure are the result of the formation of an expansive alkali-silica gel. One of the ways to minimise the effects of this damaging reaction is to use lithium compounds as an admixture to concrete mixes. Lithium ions are believed to reduce the reaction between the alkalis and aggregate or minimise damaging expansivity by modifying chemical composition of the reaction products.This paper presents the results from the tests carried out on mortars from reactive polymineral gravel with lithium nitrate according to the modified ASTM C1260 standard and ASTM C227. The findings show that lithium ions decrease mortar expansion until it reaches the levels markedly lower than those set out in the standards. A considerable reduction in the number of microcracks may indicate either lower swelling capacity of the gels or reduced reactivity of the aggregate, leading to the reduction in the quantity of damaging expansive products.

CO2 capture using fly ash from coal fired power plant and applications of CO2-captured fly ash as a mineral admixture for concrete

The utilization of fly ash as a solid sorbent material for CO2 capture via surface adsorption and carbonation reaction was evaluated as an economically feasible CO2 reduction technique. The results show that fly ash from a coal fired power plant can capture CO2 up to 304.7 μmol/g fly ash, consisting of 2.9 and 301.8 μmol/g fly ash via adsorption and carbonation, respectively. The CO2 adsorption conditions (temperature, pressure, and moisture) can affect CO2 capture performance of fly ash. The carbonation of CO2 with free CaO in fly ashes was evaluated and the results indicated that the reaction consumed most of free CaO in fly ash. The fly ashes after CO2 capture were further used for application as a mineral admixture for concrete. Properties such as water requirement, compressive strength, autoclave expansion, and carbonation depth of mortar and paste specimens using fly ash before and after CO2 capture were tested and compared with material standards. The results show that the expansion of mortar specimens using fly ash after CO2 capture was greatly reduced due to the reduction of free CaO content in the fly ash compared to the expansion of specimens using fresh fly ash. There were no significant differences in the water requirement and compressive strength of specimens using fly ash, before and after CO2 capture process. The results from this study can lead to an alternative CO2 capture technique with doubtless utilization of fly ash after CO2 capture as a mineral admixture for concrete.

The effect of the source of cement SO3 on the expansion of mortars

In order to evaluate the risk of the source and quantity of cement SO3 on the expansion properties of mortars, this paper studied the influence of Gypsum, Bassanite and clinker sulfate on the cement paste expansion and the formation of delayed ettringite. The investigation covers the mortar cured at 20°C and 80°C and stored in water. In contradiction to many studies, the results showed that the cement produced with high sulfur clinker had lower expansion than that produced with classical gypsum or high soluble Bassanite. In addition to that, we have detected that the percentage of SO3, in the cement, could increase the risk of DEF if it surpasses the level of 3.5%. Also, the curing temperature at 80°C affects the microstructure of concrete by generating cracks in the cement paste.

KINETIC MODEL TO PREDICT ULTIMATE MORTAR EXPANSION

This study reports the prediction of ultimate mortar expansion (UME) due to alkali-silica reactivity. The investigated sixteen aggregate groups with a wide range of geology and mortar expansion that were utilized in this study were obtained from two existing experimental studies. The expansions over the 28-day testing period were fitted with the ASR decay model to predict the UME and time required to reach 50%, 75%, 90% and 95% of UME. The study showed that the ultimate mortar expansion varied with aggregate mineralogy. Finally, aggregates susceptible to alkali-silica reactivity were determined based on the proposed limit of ultimate mortar expansion, and they were compared with the results obtained by the aggregate geology and expansion limits at test durations of 14 and 28 days.

Influence of cement alkalis on mortar expansion of ASTM C 1260

Influence of cement alkalis on mortar expansion of ASTM C 1260

Evaluating the effect of recycled aggregate on damaging AAR in concrete

A study examining damaging alkali–aggregate reaction (AAR) in concretes containing recycled aggregate is described. This considered masonry units, concrete, demolition waste, road planings, slate and plasterboard. Alkali release tests indicated that masonry units tended to release more alkali than recycled concrete (with higher levels generally obtained from recently produced materials), with slate and plasterboard giving least. Accelerated mortar expansion (reactivity) test results suggested there was a low risk of AAR for the materials. Concrete tests were then made using BS 812-123 exposure conditions. The concretes were proportioned (i) following the standard mixes (Na2Oeq = 7·0 kg/m3) with recycled materials replacing fine or coarse aggregate in a low-reactivity aggregate combination and (ii) at high alkali level (Na2Oeq = 5·4 kg/m3) with the materials as fine aggregate in a normal-reactivity aggregate combination. The tests for (i) gave results for the recycled materials indicating low reactivity, with classifications of non-expansive or probably non-expansive to BRE Digest 330. For (ii), expansions for the materials were mainly similar/slightly higher than those found for (i). However, recycled concrete that previously exhibited damaging AAR had greater expansions. Selected concretes were exposed at an external site for up to 8·5 years, during which observations by microscopy were carried out. These gave general agreement with the laboratory tests. The practical implications of the study are reviewed.

Cementitious properties and microstructure of an innovative slag eco-binder

Circulating fluidized bed combustion fly ash was used to activate the hydration of ground granulated blast furnace slag to produce non-cement SCA eco-binder without Portland cement (OPC). The engineering properties of SCA paste and mortar with air or water curing were evaluated. The microstructure and hydration products of the SCA binder were investigated by scanning electron microscope, and X-ray diffraction. The hydration products of SCA were ettringite (AFt), calcium silicate hydrate (C–S–H) and calcium aluminate silicate hydrate (C–A–S–H) so that the SCA paste had proper setting times, dense microstructure and high strength. The compressive strengths of SCA pastes and mortars reached up to 70 MPa at 28 days and even higher at longer ages. The early expansion of SCA paste and mortar due to the AFt formation compensated for their drying shrinkage to lead to a very low ultimate shrinkage. The SCA binder is a promising alternative to OPC.

Mechanical mechanism for expansion and crack of mortars containing basic oxygen furnace slag sand

Basic oxygen furnace slag is the main steel slag in China. This study aims to set forth the mechanical mechanism for expansion and crack of mortars made with basic oxygen furnace slag sand from compressive strength, linear expansion rate under hot-water curing condition and microscopic test. The results indicated that the expansion rate had some correlations with the strength and the rapid increase of expansion rate accompanied the remarkable decrease of compressive strength for mortars made with basic oxygen furnace slag sand. However, the expansion curve was similar to a horizontal line without decrease of compressive strength for mortars made with standard sand. Tiny cracks arose from hydration of mottled particles were the main reason resulted in the volume unsoundness of mortars made with basic oxygen furnace slag sand according to the result of XRD and the characteristics of crack. Model of expansion and cracking of mortars made with standard sand was built at last.

Effect of glass powder on microstructure of cement pastes

The effect of glass powder (GP) on the microstructure of cement pastes was studied by using mercury intrusion porosimetry, thermogravimetric and differential thermal analysis, scanning electron microscopy, energy dispersive spectrum analysis and X-ray diffraction techniques. The compressive strength and alkali–silica reaction (ASR) expansion was also tested. The test results indicated that GP can increase the compressive strength of cement pastes and control the ASR expansion of mortars. With the increase in GP content, ASR expansion decreases sharply, although compressive strength decreases a little with a large amount of GP. The characteristic pore sizes decreased with some capillary pores transforming to interstitial pores or gel pores as GP content increased. GP could diminish pore size in cement pastes, which has important significance in improving durability. Incorporating GP in cement-based materials had little effect on the kinds of hydration products, but it significantly affected the amount of hydrates, especially calcium hydroxide. The amount of calcium hydroxide reduces with the increase in curing age and GP content. The microstructure of hardened pastes containing GP was relatively dense with an abundance of calcium silicate hydrate, whose morphology was different from the gel in pure cement systems. This kind of calcium silicate hydrate gel with a low calcium/silicon ratio had a network structure formed by irregular stumpy and lamelliform gel granules. GP has high pozzolanic activity.

Alkali silica reaction in mortar formulated from self-compacting high performance concrete containing rice husk ash

In the present study, the resistance of mortar formulated from self-compacting high performance concrete containing rice husk ash (RHA)/silica fume (SF) and reactive/non-reactive aggregates to alkali silica reaction (ASR) was assessed.For the mortar containing greywacke reactive aggregate, SF is significantly more effective than RHA in reducing expansion of the mortar under accelerated testing conditions (NaOH 1M at 80°C). The increase in particle size of RHA increased the expansion of mortar. Surprisingly, the mortars containing coarse RHA, i.e. 15.6 and 7.7μm, were disrupted after 28 and 56days of immersion. However, the increase in the fine RHA (5.7μm) content decreased the expansion of mortar.For the mortar containing non-reactive basalt aggregate, the incorporation of RHA increased the expansion, and the samples containing the coarse RHA (15.6μm) cracked substantially. This indicates that RHA had paradoxical effect on ASR. The results from microscopic investigations show that RHA particles cracked substantially. The cracks also radiated from the RHA particles into the matrix, and ASR gels formed inside the RHA particles. It is suggested that to mitigate ASR by using RHA, RHA should be ground to very fine particle sizes of at least 5.7μm.

Minimum SCM requirements in mixtures containing limestone cement to control thaumasite sulfate attack

Different supplementary cementing materials (SCMs) were used in Portland-limestone cement (PLC) blends in order to achieve sulfate resistance. The resistance was evaluated by studying mortar expansion and mass change in ettringite sulfate attack (ESA) and thaumasite sulfate attack (TSA). The results showed that the PLC blends containing the Canadian standard recommended amounts of SCMs were not resistant against TSA. However, by increasing the SCM amount, the desired resistance was achieved. Additional SCM types not mentioned in CSA were found as high sulfate resistant blended PLC; among those, the ternary blends of PLC, slag, and fly ash were found to be the most resistant. Additionally, for all blends, a very good correlation between the expansion and mass change results was found.

Interfacial transition zone of cement paste-reactive aggregate in cement-zeolite mortars

Abstract Alkali-aggregate reaction is an expansive chemical reaction between the alkalis present in cement paste and minerals contained in aggregates. Mineral admixtures can mitigate the detrimental processes caused by this reaction. One of the minerals that reduce the effects of the alkali-aggregate reaction is natural zeolite. This study attempts to explain the process that takes place in the zone surrounding reactive gravel in the cement mortar made with an addition of natural zeolite. Mortar bar expansion tests were performed and a scanning electron microscope equipped with an energy-dispersive X-ray spectrometer was used to observe the paste-aggregate interfacial zone. The results confirmed the influence of the zeolite on the reduction in reactive aggregate-based mortar expansion. The microstructure of the aggregatepaste interfacial region was described and particular sub-zones varying in terms of calcium, sodium, potassium and silicon contents were determined.

Comparison of alkali–silica reactions in alkali-activated slag and Portland cement mortars

Alkali–silica reactions (ASR) in alkali-activated slag (AAS) and Portland cement (PC) mortars were studied to compare their expansions and products. ASR expansions were measured following ASTM C1260 with modified curing and exposure conditions. Scanning electron microscope equipped with an energy-dispersive X-ray analyzer (SEM/EDX) was used to characterize the ASR products in both types of mortar after 28 days of testing. The concentration of OH− in the extraction solution of all the mortars at different ages was determined by ex situ extraction method. The results showed that AAS mortars exhibited lower ASR expansion than the PC mortars when they were exposed to 1 N NaOH solution. The observation of ASR products in the AAS mortars under water and steam exposure conditions supported the presence of their minor ASR expansions, which were not observed in the corresponding PC mortars. SEM/EDX observation and analyses demonstrated obviously different morphologies of AAS mortars under different exposure conditions. The lower ASR expansion of mortars can be explained by their lower concentration of OH− in the extraction solution, which might reflect the relative alkalinity in their pore solution.