Mortar Expansion Research Articles

Prediction of ultimate expansion of ASTM C 1260 for various alkali solutions using the proposed decay model

The main purpose of this paper was to predict the ultimate mortar expansion (UME) and the time required to reach at 25%, 50%, 75%, 90% and 95% of the UME for the 1.0N, 0.5N and 0.25N NaOH solutions using the proposed ASR decay model (ADM). The expansion data, over the 98-day testing period, utilized in this study were produced from the fourteen aggregate groups having a large variation in mortar expansions. The analytical mortar expansions at the 14, 28, 56, and 98days were evaluated, and compared with those obtained by the experimental procedures. Additionally, the failure limit of UME for each alkali solution was developed to better predict the degree of reactivity of the investigated aggregates. When compared to the 14-day expansion limit, the proposed failure criteria of ultimate mortar expansion showed better correlations with the findings obtained from the previously suggested 28- and 56-day the expansion limits in evaluating alkali-silica reactivity of the investigated aggregates.

Durability of Air Entrained Cement Mortars Under Combined Sulphate and Freeze-thaw Attack

The paper deals with experimental results of combined sulphate expansion and freeze-thaw attack on air entrained (AE) and non-air entrained (nAE) ordinary portland cement mortars. After prior freezing and thawing of the 4x4x16cm mortar bars the part of them was subjected to sulphate attackof the 5% Na2SO4 solution. Another part of mortar bars was immersed in the sulphate solution for 110 days and then these bars were frozen and thawed. The resistance of nAE and AE mortars to regular sulphate and freeze-thaw attacks alone was tested as well. In order to compare damage degree of mortars in all environments, there were investigated long term linear strains (expansion), and compressive strength of mortars. Also the SEM and XRD analyses of mortars were carried out. Compared to the individual sulphate attack alone, prior freeze-thaw and following it sulphate attack affected significant acceleration of sulphate expansion of nAE and AE mortars as well, despite much better resistance of AE mortars to freezing and thawing. However, the prior sulphate attack significantly reduced AE mortars resistance to freezing and thawing. The SEM analysis showed that air voids in AE mortars were partially filled with ettringite. Its precipitation in air voids of AE mortars caused that the volume of air was diminished and freeze-thaw resistance of AE mortars was significantly decreased and it was as low as resistance of nAE mortars was. The complete destruction of AE mortars subjected to sulphate attack alone occurred earlier than that of nAE mortars did. Based on SEM analysis results it is suggested that lower sulphate resistance of AE mortars was due to higher porosity of the air void-paste interface and its higher initial w/c ratio compared to ‘bulk paste’ farther away from.

High-Performance Grouting Mortar Based on Mineral Admixtures

A study on high-performance grouting mortar is reported. The common mortar was modified by mineral admixtures such as gypsum, bauxite, and alunite. The effects of mineral admixtures on the fluidity, setting time, expansion, strength, and other properties of mortar were evaluated experimentally. The microstructure of the modified mortar was characterized by X-ray diffraction, scanning electron microscopy, and mercury intrusion porosimetry. Moreover, the expansive performance and strength of the grouting mortar were verified by anchor pullout test. The results show that the best conditions for gypsum-bauxite grouting mortar are as follows: a water-to-binder ratio of 0.3, a mineral admixture content of ~15%, and a molar ratioKof 2. The ultimate bearing capacity of the gypsum-bauxite grouting mortar anchor increased by 39.6% compared to the common mortar anchor. The gypsum-bauxite grouting mortar has good fluidity, quick-setting, microexpansion, early strength, and high strength performances.

Waste glass sludge as a partial cement replacement in mortar

This paper presents the results of a study conducted to evaluate the possibility of utilizing the waste glass sludge (WGS) from the cutting and polishing process of glass plates, as a partial replacement of cement. A total of seven mortar mix proportions were prepared, by replacing ordinary Portland cement with WGS and/or fly ash (FA). The influences of WGS and FA on the compressive strength of mortars and ASR expansion of mortars were investigated. In addition, X-ray diffraction analysis was performed, to evaluate the pozzolanic activity. The results show that the incorporation of the WGS yields mortars with improved strengths at the later age (28days), in comparison with that of a control mortar (ordinary Portland cement only); while the WGS caused a lower early strength than that of control, but higher than that of mortars containing FA. The ASR expansion of the mortars can be reduced by incorporating WGS as effectively as by fly ash. It is found that the consumption rate of calcium hydroxide for the paste with the WGS was faster than that of paste with FA, up to 28days. These results indicate that the WGS has a higher reactivity than FA; and therefore, the WGS can be used as a pozzolanic admixture in cement composites.

Corrosion Resistance of 50 Years Concrete Exposed to Saline Areas

The Hong Run petrochemical oil depot is located in a saline area in the north of Weifang, where the contents of chloride and sulfate in this area are very high. Due to the rigorous environmental conditions, concrete with 50 years durability and C40 strength grade was prepared. A kind of corrosion resistance concrete with high performance superfine mineral powder and high performance pumping agent was developed to adapt to the conditions in saline areas. The chloride-penetration resistance ability was investigated by the test of chloride ion rapid electric transport (ASTM C1202). The concrete compressive strength and mortar expansion rate under continuous immersion in four different corrosion solutions was studied. The results showed that the chloride-penetration grade is very low. The compressive strength is high and the mortar expansion rate lower than 0.1%.

Effect of particle size on alkali–silica reaction in recycled glass mortars

The effect of particle size on alkali–silica reaction (ASR) was investigated to clarify the difference in long-term ASR expansions in mortars using recycled green and brown glass as fine aggregates. Test results revealed that green particles of 1.18 and 2.36mm showed the highest reactivity while the other sizes resulted in relatively low ASR expansions. Brown glass less than 2.36mm did not result in large ASR expansion. Furthermore, different ASR suppressors were explored to suppress ASR expansion in mortar using 1.18mm green glass particles. These included supplementary cementitious materials, steel fiber reinforcement and lithium compounds.

Modelling The Effects of Aggregate Size on Alkali Aggregate Reaction Expansion

This work aims at developing models to predict the potential expansion of concrete containing alkali-reactive aggregates. The paper gives measurements in order to provide experimental data concerning the effect of particle size of an alkali-reactive siliceous limestone on mortar expansion. Results show that no expansion was measured on the mortars using small particles (0.5-1.0 mm) while the particles (1.0–2.0 mm) gave the largest expansions (0.217%). Two models are proposed, the first one studies the correlations between the measured expansions and the size of aggregates, the second one calculates the thickness of the porous zone necessary to take again all the volume of the gel created.

Hydration characteristic, thermal expansion and microstructure of cement containing nano-silica

The effect of nano-silica (NS) on the hydration characteristics, thermal expansion and microstructure of cement pastes and mortars was studied. OPC was replaced with NS up to 6.0%. The presence of NS increases the required water of standard consistency and elongated the setting times. The results of chemically combined water, free portlandite, pH, bulk density, compressive strength and thermal expansion showed that NS contents up to 5.0 mass% improve the physico-chemical and mechanical properties of cements. NS behaves not only as filler to improve the microstructure, but also as an activator to promote the pozzolanic reaction, which enhances the formation of hydrated products. It was concluded that partially substitution of OPC up to 5 mass% NS improves the mechanical and microstructural characteristics in comparison with the neat OPC paste up to 90days.

Evaluation of nitric and acetic acid resistance of cement mortars containing high-volume black rice husk ash

This paper presents the performance of cement mortar containing black rice husk ash (BRHA) under nitric and acetic acid attacks. The BRHA, collected from an electrical generating power plant that uses rice husk as fuel, was ground using a grinding machine. The compressive strength loss, weight loss, and expansion of mortars under nitric and acetic acid attack were investigated. The test results of BRHA properties in accordance with the ASTM C 618 standard found that the optimal grinding time was 4 h as this achieved a Blaine fineness of 5370 cm2/g. For parametric study, BRHA were used as a Portland cement Type 1 replacement at the levels of 0%, 10%, 20%, 30%, 40%, and 50% by weight of binder. The water-to-binder ratios were 0.55, 0.60, and 0.65. From test results, when the percentage replacements of BRHA in cement increased, it was observed that the strength loss and weight loss of mortars containing BRHA under acetic acid attack were higher than those of the mortars against nitric acid attack. It was found that, of the various BHRA mortars, the strength loss and weight loss due to nitric and acetic acid attacks were the lowest in the mortar with 10% BRHA replacement. For 10%, 20% and 30% BRHA replacements, the rate of expansion of the BRHA mortar decreased when compared with the control mortar. For the mortars with other percentage replacements of BRHA, the rate of expansion increased. Furthermore, the effective water-to-binder ratios of control and BRHA mortars were the primary factor for determining the durability of mortar mixed with BRHA.

Change of the Coefficient of Thermal Expansion of Mortar Due to Damage by Freeze Thaw Cycles

This paper presents the experimental methods and findings in obtaining the strain behavior of mortar during freezing and thawing cycles (FTC) at the meso-scale under fully saturated condition and the coefficient of thermal expansion (CTE) and elastic modulus of mortar after FTC tests. A heat-cool cycle test comparing an oven-dried and undried mortar was also performed prior to the FTC test, confirming that oven drying at 105°C does not affect the CTE of samples, thereby ensuring the reliability of the results. During FTC with constant moisture content, a limitation in the increase in tensile strain was observed and this tensile strain decreased until contraction was observed. The contraction is attributed to the removal of gel pore water arising from negative pressures. Due primarily to the absence of available water supply, the displaced pore water cannot be refilled, which results in contraction at the end of the FTC. More importantly, the results show that after FTC, the CTE of frost damaged mortar increases while its elastic modulus decreases, primarily owing to microcracking when frost damage sets in. Microcracks act as broken bridges that can detach the aggregate from the hardened cement paste and in effect reduces the thermal restraints that each part (fine aggregate and cement paste) exerts on the other. The hardened cement paste can then expand/contract more freely under temperature variation, and thus can significantly affect (increase) the CTE of the whole composite (mortar). Further, stress transfer in the material is prevented due to microcracking resulting in elastic modulus reduction.

Time Series analysis for prediction of ASR-induced expansions

The aim of this study was to predict and classify ASR reactivity of mortar bars submerged in 1,0.5 and 0.25N NaOH solutions. The experimental expansion data were recorded from the mortar specimens prepared with twelve different aggregate groups for the three alkali solutions. The dataset were then fitted in a Time Series (TS) regression model to predict the ASR-induced expansion of each aggregate group for up to 98days. The results showed that, regardless of aggregate source, the TS model was very suitable in prediction of mortar expansions when compared to those obtained experimentally. The ASR classification of the investigated aggregates obtained from the predicted expansions of the TS regression model was nearly identical to the classification determined by using experimental mortar expansions.

Expansion of Cement Mortar Mixing Expansive Agent under Different Curing Conditions and Compressive Strength in Constrained Conditions

The expansion of cement mortar mixing expansive agent under standard curing and membrane curing conditions and compressive strength in constrained conditions are studied in this paper. Results show that the early expansion effect of calcium sulphoaluminate hydrate-calcium hydroxide expansive agent is obvious, mid-to late effect of magnesia expansive agent increase clearly. Compare with standard curing, the shrinkage of the basic cement mortar increase and expansion effect of expansive agent reduce under membrane curing. The expansion effect of expansive agent B is good and persistent under membrane curing, its applicable to used in the closed environment, such as concrete filled steel tubes. The compressive strength of mortar with expansion agent is a little more than the basic mortar under the condition of limit.

A nonlinear meso–macro approach to modelling delayed ettringite formation and concrete degradation

We show how a two-scales FE model—within a sequential approach—leads to consistently simulate the DEF macroscopic consequences: cracks pattern and opening, residual modulus decrease. The mesoscopic part of this model is adapted to heterogeneous materials and is based on two kinematics enrichments. The first one leads to a very fast meshing process along the randomly chosen set of aggregates and, the second leads to directly compute the cracks openings. Assuming DEF is driving to a progressive and homogeneous mortar expansion, we show how the macroscopic—concrete—expansion as well the cracks pattern are consistent with the experiments. For the latter we are interested in the characterization of the aggregates effect on the amplitude of DEF swelling, so that we focus on parameters such as the size and the volume fraction of granular inclusions.

The effect of natural pozzolan on delayed ettringite formation of the heat-cured mortars

Delayed Ettringite Formation (DEF) is an internal sulfate attack caused by early age heating to a temperature of over 70°C. In this paper, the effect of natural Algerian pozzolan on the expansion of cement mortars caused by DEF was investigated. For this purpose, a portion of cement was replaced by natural pozzolan, with three different dosages (10%, 20% and 30%) and finenesses (fine, medium, and coarse). The results obtained highlighted the significant effects of natural pozzolan on DEF and the correlation existing between the expansion of the heat-cured mortars and the evolution of their mechanical properties.

Influence of clinker sulfate on cement paste external sulfate attack

This paper aims to clarify the influence of the clinker sulfate on external sulfate attack of cement paste. The investigation shows that the clinker sulfate does not have any direct influence on the resistance of cement to external sulfate attack. Indirectly this sulfate reduces the amount of tricalcium aluminate (C3A) and tricalcium silicate (C3S), generating an improvement in the level of cement resistance to external sulfate attack. The mortar expansions, after 1 year of storage in 5% sodium sulfate (Na2SO4) solution, verify the mineralogical results. Additionally the investigation indicates that the combination of the three techniques – X-ray diffraction analysis, scanning electron microscopy and graphical treatment of microanalysis by energy-dispersive X-ray spectroscopy – leads to a better understanding of the causes of paste deterioration by external sulfate attack.

Reduction of alkali−silica reaction expansion of mortars by utilisation of pozzolans

In this study the effects of natural and artificial pozzolans on alkali–silica reaction expansion of mortars were investigated by using the accelerated mortar bar test method in accordance with the ASTM C 1260. For this purpose, four natural pozzolans – ignimbrite powder (IG), perlite powder (PE), pumice powder (PU) and zeolite powder (ZE) – were used as cement at replacement levels of 0, 5, 10, 15, 20, 25, 30, 35 and 40% by weight of ordinary Portland cement. Four artificial pozzolans – fly ash (FA), brick powder (BP), silica fume (SF) and aerated concrete powder (AP) – were used at replacement levels of 0, 5, 10, 15, 20 and 25% by weight. The expansions of mortar bars were reduced as the replacement ratios of each natural and artificial pozzolans were increased, with the exception of specimens with a replacement level of 15, 20 and 25% AP. It is determined that at comparable replacement ratios SF is the most effective among the pozzolans used and is followed by PU, ZE, IG, PE, FA, BP and AP respectively.

セメント系材料により生成される水和物の相組成とASR膨張抑制効果の関係

アルカリシリカ反応（ASR）を最も効果的に抑制するのは鉱物質混和材（SCM）であり，空隙水のpHの低下がその理由と推定されるが，直接的に証明されていない．SCMをセメントの一部と置換する機構をセメントの水和反応解析を基に推定した相組成と空隙水の溶解平衡関係から検討するとともに，モルタルの膨張量試験との比較から，ASR抑制効果との関係について考察した．これらの結果から，セメントの一部をSCMにより置換したモルタルのASR抑制機構は低Ca/Siモル比のC-S-Hのアルカリ固定に伴う空隙水のOH-濃度低減という説が最も合理的と考えられた．これらの結果を基にSCM置換率とOH-濃度の関係を整理し，高反応性の骨材に対してはより厳しい抑制対策が必要であることを考察した．

Expansion of mortars with gypsum contaminated fine recycled aggregates

This study evaluates the expansivity of fine recycled aggregates mortars depending on the type of Portland cement, the consistency and the equivalent of acid soluble sulphates (SO3) content. For that, an experimental campaign divided in two phases was performed. In the first phase, the cement pastes were produced and tested by means of X-rays diffractions in order to analyze the hydrated compounds formed over time. In the second phase mortars samples were cast in order to assess the physical and mechanical properties as well as the expansion over time. The results showed that incorporation of gypsum contaminated fine recycled aggregates with SO3 contents up to 2.9% by weight does not compromise the durability in mortars, regardless of the cement types studied in this study, the consistency and the contaminant present.

The influence of aluminium on the dissolution of amorphous silica and its relation to alkali silica reaction

It is known that the addition of supplementary cementitious materials (SCMs) in concretes reduces or even stops expansion due to alkali silica reaction (ASR). It has been widely shown that the main mechanism controlling ASR in blends is the alkali fixation capacity of silica rich C–S–H, which lowers the pH of the pore solution. The role of alumina additions is less clear. It was shown in a previous paper [1] that the alumina present in certain SCMs does not further reduce the alkalinity of the paste pore solution. It is proposed here that aluminium acts directly on the reactive phases of the aggregates. Aluminium species, present in the pore solution, are absorbed on the silica surface and limit the dissolution of amorphous silica of the aggregates, restricting ASR. The effect of aluminium was demonstrated through a study of mortar expansion and SEM image analysis of reactive aggregates in simulated pore solutions.

Mechanism of expansion of mortars immersed in sodium sulfate solutions

The mechanisms behind the expansion of samples immersed in solutions containing sulfate ions have been controversial. Expansion is believed to originate in the formation of ettringite, but it is not possible to find any direct correlation between these two processes or to relate expansion purely to the increase in solid volume. Crystallization pressure is considered to be the most likely mechanism. A key aspect of this mechanism is the existence of supersaturation in the solution with respect to the growing crystal and it is not possible to directly measure the composition of the pore solution at different points within the specimen.In this paper we present a refinement of the crystallization pressure hypothesis to explain sulfate related expansion. We provide evidence that expansion is related to the transformation of monosulfate crystals embedded in the C-S-H to ettringite. Initially incoming sulfate reacts with aluminate containing hydrates in large pores to give ettringite without expansion. During this process the composition of the solution is buffered by the precipitation of solids so the rate of ingress does not depend strongly on the solution composition. After all this “freely available” aluminate has reacted, the concentration of sulfate ions in the pore solution increases, as indicated by the rise of sulfate absorbed on C-S-H. When the solution concentration reaches a critical level it provides the driving force for the precipitation of ettringite crystals in small pores within the C-S-H. Due to the confinement and the supersaturation of the solution this formation of ettringite leads to expansion of the paste.