Mortar Expansion Research Articles

Feasibility and Characterization Mortar Blended with High-Amount Basic Oxygen Furnace Slag.

Basic oxygen furnace slag (BOFS) was ground to three levels of fineness as a replacement for cement at weight proportions of 10, 30, 50, and 70 wt.%. Fineness and weight proportion were shown to have significant effects on the flowability and setting time of the mortars. The expansion of BOFS mortars increased with an increase in the proportion of cement replaced, thereby exacerbating the effects of cracking. Optimal mechanical properties were achieved when 10 wt.% of the cement was replaced using BOFS with fineness of 10,000 cm2/g. The compressive strength of BOFS mortar is similar to that of ordinary Portland mortar, which makes BOFS suitable for the partial replacement of cement as a supplementary cementitious material. Scanning electron microscopy results revealed that the reaction of CaO with H2O results in the formation of C–S–H colloids, whereas the reaction of SiO2 with Al2O3 produces C–A–S–H colloids. The use of BOFS as a partial replacement for Portland cement could make a tremendous contribution to the steel industry and help to lower CO2 emissions.

Mechanical Properties and Corrosion Resistance of Cement Concrete Containing Sea Sand or Sea Water

ABSTRACT Through the test of 27 groups of specimens, the influence law on compressive strength and expansion under sea salt corrosion by type of cement, fly ash substitute rate of cement, fly ash substitute rate of fine aggregate, water-binder ratio, type of fine aggregate, and immersion method were analyzed. The corrosion resistance of reinforced concrete under sea water attack was also studied in this research. The experimental results indicate that the influence of various factors on the compressive strength is correlative, and the interaction effects of the type of cement and type of fine aggregate, type of cement and immersion method on the compressive strength are correlative; fly ash substitute rate of fine aggregate, water-binder ratio, type of fine aggregate and immersion were all had significant effects on the expansion at each age. The immersion method had the most significant effect on the expansion. The type of fine aggregate has a significant effect on all tests, but other more correlative factors can be used to improve the deterioration of cement mortar caused by sea sand. Replacement of 10% or 20% aggregate by fly ash gives no apparent improvement in preventing the expansion of cement mortar in sea water exposure. The concrete test results indicate that no serious detrimental effect was found for the corrosion inhibitor in reinforced concrete.

Influence of Multi-Phase Carboxylate Salt on Mortar Properties under Sulfate Environment

A novel multi-phase carboxylate (MPC) salt was prepared by free radical polymerization. Influence of MPC salt on properties of mortar under sulfate environment was investigated. The results from static solution soaking and wet-dry cycling tests indicated that MPC would not bring negative effects on strength and shrinkage of mortar. In particular, MPC was able to reduce the strength loss as a result of inhibiting the generation and growth of ettringite in static solution soaking test. The crystal expansion of AFt was reduced since the Ca2+ dissolution and SO42- ingress were less. Meanwhile, the strength loss of mortar under sulfate wet-dry cycling could be reduced as well by MPC. MPC inhibited the growth of CaSO4·2H2O crystals by replacing the functional groups. The growth of micro-cracks in cement paste was inhibted and the the risk of crystal expansion and destruction of mortar was reduced. It was believed that MPC exhibited an excellent sulfate attack resistance for mortar.

Effect of Addition Rate of Expansive Additive on Autogenous Shrinkage and Delayed Expansion of Ultra-High Strength Mortar

Effect of Addition Rate of Expansive Additive on Autogenous Shrinkage and Delayed Expansion of Ultra-High Strength Mortar

Extension of the chemical index model for estimating Alkali-Silica reaction mitigation efficiency to slags and natural pozzolans

Supplementary cementitious materials (SCMs) can mitigate alkali silica reaction (ASR) but the level of cement replacement required is difficult to estimate for a particular SCM. The Chemical Index Model was recently proposed to estimate the relation between mortar expansion and the chemical compositions of cement and fly ash but has not been tested extensively for use with other SCMs. This study uses natural pozzolans and blast furnace slags, in addition to fly ashes, with two portland cements and a reactive aggregate to evaluate the effectiveness of the model to estimate 14-day ASTM C 1567 expansion. The reactivities of different oxides are discussed. Model parameters are calibrated for use with mortars containing slags or natural pozzolans. Improvements are suggested to the optimization strategy in the model. Errors in the estimated minimum cement replacement to limit expansion to 0.1% are significantly lowered when the calibrated model is used with these improvements.

The application of a new oxidation mortar bar test to mixtures containing different cementing systems

The effects of different cementing systems on the expansion of mortars containing iron sulphide-bearing aggregate was studied. Using a recently developed oxidation mortar bar test, the results showed that cementing systems containing low-calcium fly ash, metakaolin, slag, high-sulphate resisting Portland cement, or low heat of hydration Portland cement could reduce the expansion by 50–85%. The main suggested mechanisms behind the reduced expansion is the more refined pore structure of samples with SCMs, and the reduced C3A of low heat of hydration Portland cement. The refined pore structure reduces the permeation of the oxidizing solution into the samples. The similarity of this to penetration of oxygen into concrete under field exposure needs to be determined. Soaking the samples for >3 h in the oxidizing agent can produce excessive expansion – not related to oxidation of iron sulphide phases – in samples with cementing blends containing reactive alumina such as metakaolin.

Use of Coal Fly Ash or Glass Pozzolan Addition as a Mitigation Tool for Alkali-Silica Reactivity in Cement Mortars Amended with Recycled Municipal Solid Waste Incinerator Bottom Ash

Municipal solid waste incinerator bottom ash was evaluated for its alkali aggregate reactivity in cement mortars. Subsequently, two wastes were evaluated as supplementary cementitious materials for their efficacy in mitigating expansive alkali-silica reactions in cement mortars amended with bottom ash. Three bottom ashes were incorporated into mortar bars as 15, 30 and 50% replacements of non-reactive sand. Control MSWI amended mortars were compared to those containing coal fly ash and glass pozzolan (synthetic glass). Dimensional expansion of the mortars was measured over 14 days to quantify the extent to which the recycled coal fly ash and glass pozzolan mitigated the alkali reactivity of the ash-amended mortar specimens. Average expansions of the ash-amended mortars ranged from 0.10 to 0.40%, suggesting that ash components reacted expansively in an alkaline environment. Microscopic analysis was used to complement the data and confirm the presence of silica-rich gel within glass fragments of the ash, as well as cracking of the aggregates. Supplementary cementitious materials (class F coal fly ash, glass pozzolan) mitigated expansion of the mortars by 90% on average, likely through consumption of the alkalis in the paste pore water.

Use of basic oxygen furnace slag fines in the production of cementitious mortars and the effects on mortar expansion

The purpose of this study was to examine the properties of ordinary Portland cement (OPC) and alkali-activated slag (AAS) mortars produced with basic oxygen furnace (BOF) slag fines, and to reveal the effects of BOF slag fines on the expansion of the cementitious mortars. The use of BOF slag fines in OPC mortars significantly reduced the compressive strength and slightly increased the volume expansion of the mortars. Significant changes in mineralogical composition were observed in the OPC mortars produced with BOF slag fines after autoclaving. On the other hand, the AAS mortars produced with BOF slag fines had compressive strength comparable to normal OPC mortars, and their volume expansion was much lower than the AAS-Control and all the OPC mortars. The mineralogical compositions of the AAC mortars before and after autoclaving were almost identical. The results of this study indicate that the BOF slag fines are suitable to partially replace the binder for the production of AAS mortars, and the resulting AAS mortars have high volume stability.

Blast Furnace Slag Addition Effects on Delayed Ettringite Formation in Heat-cured Mortars

Reducing expansion due to Delayed Ettringite Formation (DEF) is becoming an important issue that must be taken into account, when producing heat-cured concrete. Mineral additives used as partial cement replacement should help in achieving the desired aspect. Based on an ongoing experimental program, this research emphasizes on the effect of Blast Furnace Slag (BFS) on the expansion of cement mortars caused by DEF. For this purpose, mortar prisms in which Portland cement was replaced by BFS, with three different replacement levels (10,20 and 40%) and two finenesses degree (400 and 500 m2/kg) were tested in length change, dynamic elasticity modulus and compressive strength over more than 750 days. Results showed that the efficiency of blast furnace slag in controlling expansion related to DEF was conditioned by its levels of replacement.

Research on the Expansion Characteristics and Compressive Strength of Mortars Containing Circulating Fluidized Bed Combustion Desulfurization Slag

Circulating fluidized bed combustion (CFBC) desulfurization slag is a waste residue discharged from coal power plants. In this article, expansion characteristics and compressive strength of mortars containing CFBC desulfurization slag were evaluated, subjected to mechanical grinding time, the amount of additive, and chemical activation. Correlations between the linear expansion rate and compressive strength were investigated. The hydration products of cement‐slag cementitious system were analyzed by X‐ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that mechanical grinding can increase both the expansion and compressive strength of mortars containing CFBC desulfurization slag, and the compressive strength and linear expansion can develop in coordination. While increasing the amount of the fine desulfurization slag, the linear expansion rate increases, and the compressive strength reaches to the maximum when the amount is 30%. Moderate sodium sulfate as an activator can both promote the compressive strength and increase the expansion of mortars.

The Behavior of Portland Limestone-Calcined Clays Cement at 5°C

The effect of calcined clays of the swelling type, on the strength and expansion behavior of Portland limestone cement is studied at 5°C. Local clays were thermally activated by burning one hour at 900 °C and were ground to a Blaine of 2842 (cm2/g). The pozzolanic reactivity of the activated clays was defined chemically and according to ASTM C311/C311M-13. Portland limestone cement was prepared by replacing 30% CEM I 42.5 N by limestone powder. Pozzolanic cements were prepared by replacing 10 and 20% of the limestone powder by calcined clays, the mixes were used to replace 30% of CEM I. Mortars specimens pre-cured for 28-day long as well as for a short period of one day, were immersed in sulfate solutions at 5°C for time up to 90 days. The compressive strength and length change were measured for the samples.The results show that replacement of limestone with calcined clays improves the compressive strength and the expansion of Portland limestone cement mortars in water and sulfate solutions. Ettringite was detected in the expanded mortars and no thaumasite formed. The results are interpreted in terms of the mechanism of thaumasite formation.

Effect of Addition Rate of Expansive Additive on Autogenous Shrinkage and Delayed Expansion of Ultra-High Strength Mortar

Effect of Addition Rate of Expansive Additive on Autogenous Shrinkage and Delayed Expansion of Ultra-High Strength Mortar

Influence of ground waste expanded perlite on the reaction of siliceous aggregates with sodium and potassium hydroxides

Paper presents results of investigation on the influence of ground waste expanded perlite on the mitigation of alkali – silica reaction in cement mortars. Crushed quartz glass was used as model reactive aggregate. Natural reactive aggregate containing radiolarite was also used. Obtained results showed, that addition of ground waste expanded perlite to mortars containing reactive aggregates resulted in significant reduction of alkali – silica reaction. Expansion of mortars soaked in sodium hydroxide at elevated temperature, according to modified ASCT C1260 test was markedly lower comparing reference samples without perlite addition. Examination of mortars and pastes with ground waste expanded perlite addition confirmed its pozzolanic properties. Increased C-S-H phase content together with decreased permeability of the mortars and decreased calcium hydroxide content are most probably the reasons for better durability of perlite bearing mortars towards alkali – silica reaction.

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Effects of Binary and Ternary Blended Cements Made from Palm Oil Fuel Ash and Rice Husk Ash on Alkali–Silica Reaction of Mortar

Alkali–silica reaction (ASR) of binary and ternary blended cement mortars made from fine particles of palm oil fuel ash (PA) and rice husk ash (RA) was investigated. Portland cement type I was replaced by PA, RA, and RA mixed with PA at rates of 10, 20, 30, and 40% by weight of binder and was used for casting mortar to investigate compressive strength and expansion due to ASR. After finishing ASR test, microstructures of the mortars due to ASR were also investigated by scanning electron microscope and energy-dispersive X-ray spectrometer. The results showed that PA and RA are good pozzolans considering in terms of compressive strength. For ASR results, the expansions of PA mortars due to ASR were lower than control mortar, while the mortars containing RA had very high expansion and many cracks. However, RA–PA mortars provided lower expansion due to ASR than RA mortars at the same rates.

Prediction of expansion of electric arc furnace oxidizing slag mortar using MNLR and BPN

The present study established prediction models based on multiple nonlinear regressions (MNLRs) and back-propagation neural networks (BPNs) for the expansion of cement mortar caused by oxidization slag that was used as a replacement of the aggregate. The data used for the models were obtained from actual laboratory tests on specimens that were produced with water/cement ratios of 0.485 or 1.5, within which 0%, 10%, 20%, 30%, 40%, or 50% of the cement had been replaced by oxidization slag from electric-arc furnaces; the samples underwent high-temperature curing at either 80oC or 100oC for 1-4 days. The varied mixing ratios, curing conditions, and water/cement ratios were all used as input parameters for the expansion prediction models, which were subsequently evaluated based on their performance levels. Models of both the MNLR and BPN groups exhibited R2 values greater than 0.8, indicating the effectiveness of both models. However, the BPN models were found to be the most accurate models.

Influence of cement alkalis on mortar expansion of ASTM C 1260

The main objective of this study was to evaluate the influence of three dosages of cement alkalis, such as 0·42, 0·84 and 1·26% Na2Oeq, on the alkali–silica reactivity-induced expansion of mortar bars prepared with 14 aggregate groups for 1·0, 0·5 and 0·25 N sodium hydroxide solutions at test durations of 14, 28, 56 and 98 d. For each alkali solution, the percentage contribution of cement alkali, test duration and their interaction to mortar expansion was also evaluated. The study revealed that, regardless of aggregate mineralogy, the influence of cement alkalis on mortar expansion depended mainly on the alkali solution concentration and test duration. The effect was more severe for the reduced concentration of alkali solution and early test duration, whereas the influence was minor for higher concentrations of alkali solution and extended test durations. Elevating cement alkalis resulted in a greater increase in the expansion of reactive aggregates for 0·25 N sodium hydroxide as compared to that of innocuous aggregates.

Study on the treatment of BOF slag to replace fine aggregate in concrete

Excessive free lime in the BOF slag will react with water and causes serious expansion, and thus, results in its reutilization difficulty. In this study, scrubbing attrition and chelating reagent treatment were used to remove free lime from BOF slag. After removing free lime, the BOF slag was used as fine aggregate for making cement mortar. Under different curing periods, the specimens were characterized for their physical and mechanical properties, ultrasound conduction velocity, and volume expansion. By reducing free-calcium oxide through attrition and chelating processes, the expansion rate of specimen can be reduced to 0.16%. The compressive strength and flexural strength of cement mortars prepared with BOF slag can reach 45.4MPa and 7.1MPa, respectively. The test results suggested that the scrubbing and chelating treatments can effectively remove free-calcium oxide and improve expansion and strength development of concrete mortar.

Effect of pulverized fuel ash and CO2 curing on the water resistance of magnesium oxychloride cement (MOC)

This paper presents a study on the use of pulverized fuel ash (PFA) to improve the water resistance of magnesium oxychloride cement (MOC). Strength retention coefficients and volume stability were tested to evaluate the water resistance of MOC, in which the addition of PFA resulted in a remarkable improvement. The characterization of hydration products before and after water immersion was carried out using quantitative X-ray diffraction (QXRD), thermogravimetric (TG), Fourier-transformed infrared spectroscopy (FTIR) and scanning electron microscope (SEM). With the Q-XRD analysis, it was shown that the addition of PFA could result in the great increase of the amount of amorphous phase during air curing. This amorphous gel was identified as a mixture of magnesium-chloride-silicate-hydrate gel (M-Cl-S-H gel) and magnesium-chloride-hydrate gel (M-Cl-H gel) by elemental mapping scanning. It suggested that PFA could not only react with MOC to form M-Cl-S-H gel, but also change the morphology of magnesium oxychloride. The generation of insoluble M-Cl-S-H gel and M-Cl-H gel and densification of the microstructure contributed to the improvement of the water resistance of MOC. The MOC mortar expanded during air curing due to the hydration of excess MgO. Water immersion led to more expansion of MOC mortar as a result of the continuously hydration of excess MgO and the formation of Mg(OH)2. Adding PFA could increase the expansion of MOC mortar during air curing, which may because the amorphous gel could remain more water and benefit to the hydration of MgO. While, the addition of PFA could decrease the expansion of cement mortar during water immersion perhaps due to the reduction of the content of excess MgO and the insoluble amorphous-gel-layer that protect the MgO from hydration. Moreover, CO2 curing could further improve the performance of the PFA-blended MOC due to the formation of a higher content of amorphous gel.

Ultrasonic and impact spectroscopy monitoring on internal sulphate attack of cement-based materials

An exhaustive monitoring of an internal sulphate attack of Portland cement-based materials is addressed. Four series of Portland cement mortars with different amounts of gypsum (0%–2% SO3 respect to the cement by mass) were monitored by means of physical, microstructural and non-destructive tests, studying specimens with a low expansion rate to examine the sensitivity of the applied techniques. The expansion analysis has shown the suitability of a fitting model, allowing the examination of two characteristic parameters: the characteristic time of the expansion reaction and the maximum amplitude of the expansion. In the mechanical analysis, higher values of Rc and Rf were attained as the gypsum content decreased. A microstructural analysis (thermogravimetry and FESEM) supported ettringite formation and expansion process. These results have been correlated with non-destructive tests: impact resonance acoustic spectroscopy and ultrasonic measures. The dynamic modulus and ultrasonic pulse velocity have closely predicted the stiffness of the specimens. The total material attenuation (absorbed energy of the chirp signal ultrasonic wave) presented different trends, showing clear differences for the most damaged series (2% SO3). Attenuation supplied interesting information about the hardening process and the microcracking effect due to a mortar expansion higher than 0.04%. The novelties of this study are the exhaustive monitoring of an internal sulphate attack, as well as the examination of the sensitivity of brand new NDT techniques when this damage process overlaps with the curing process.