Fresh Mortar Research Articles

Geopolymer Mortar with the Tailings from the Fundão Dam Rupture

The extraction of iron ore generates large amounts of tailings. In addition to other solutions to avoid storing this material in dams, it is important to use these tailings as raw materials for the manufacturing of consumer goods. One possible solution is to use geopolymer cement in mortars for civil construction with employment of the tailings as substitute for usual sands. Geopolymers are produced from alkaline activation of aluminosilicates. They can incorporate a larger amount of tailings than the Portland cement. The tailings from the rupture of the Fundão dam, which were retained in the water reservoir of the Candonga hydropower plant were characterized as a fine aggregate for civil construction and used to obtain geopolymer mortar. Metakaolin was mixed with an alkaline solution of sodium silicate and sodium hydroxide to form a paste. The tailings were added and uniformly mixed to this paste. Two series of experiments were conducted with addition of 40 and 60 wt% of tailings to the geopolymer paste. The fresh mortars were placed in cylindrical molds. The samples were left to harden at room temperature or at 60&degC for 24 hours and demolded. After hardening, the samples were cured at room temperature for 7 and 28 days. The samples were characterized by their compressive strength, water absorption, and density. The results were analyzed according to a 23 factorial design with the factors: composition (amount of tailings added to the mortar), hardening conditions, and curing time. For all responses (compressive strength, water absorption, and density), the results show a complex behavior with influence of the factors and their interactions. Compressive strengths from 19 to 43 MPa, water absorptions from 19 to 41 wt%, and densities from 1.60 to 2.11 g/cm3 were observed. These properties can be controlled by adjusting the levels of the factors according to empirical models. This mortar can be considered for applications in civil construction.

Effect of redispersible polymer powders on selected mechanical properties of thin-bed cementitious mortars

Modern mortars are complex multi-component systems. Among the mortar components, redispersible polymer powders (RDPs) play a unique role. They improve the rheology of fresh mortar while providing flexibility and tensile strength after it has hardened. The impact of polymeric binders on mortar properties has been and is currently the subject of intensive research. This paper describes how the use of different redispersible polymer powders affects cement mortars’ selected properties, i.e., crack bridging ability, adhesion determined by measurement of tensile strength and transverse deformation. Results show that all of the RDPs tested positively affect the properties of the examined system. The most significant increase in the mortar’s tensile adhesion strength was observed for the system with vinyl acetate homopolymer, the lower one for the systems with styrene-acrylic heteropolymers and vinyl acetate and ethylene heteropolymers. All tested redispersible polymer powders in the considered system increase the ability to bridge cracks in cement mortar. However, the smallest increment is observed for the acrylic homopolymer and styrene-butadiene heteropolymer. Other RDPs similarly increase the mortar’s cracks bridging ability under test defined as the ability of the hardened material (mortar) to stop the spread of cracks without damaging it. The results obtained for thin-bed cement mortars in terms of crack bridging ability were evaluated comparing the requirements for water-impermeable products. All examined RDPs showed a similar effect on the transverse deformation value of cement mortar.

A Study on the Mechanical Properties of the Hybrid Fiber-Reinforced Mortar Using the Macro Steel and Micro Carbon Fibers

In the present study, an experiment was conducted to investigate the mechanical properties such as fluidity, compressive strength and flexural performance (flexural strength and toughness) of a single fiber-reinforced mortar (FRM) using only macro steel fiber (SF) or micro carbon fiber (CF) with different material properties and SF-CF hybrid FRM using a mixture of macro SF and micro CF. The specimens incorporated macro SF and micro CF in the mix proportions of 100-0%, 75-25%, 50-50%, 25-75% and 0-100% by volume at a total fiber volume fraction of 1.0%. Their mechanical properties were further compared and reviewed with the plain mortar at 28 days of age. The experimental results of fresh mortar showed that the table flow of mortar using only macro SF was slightly reduced compared to plain mortar, whereas the table flow of mortar using only micro CF and SF-CF hybrid mortar decreased significantly with increase of micro CF. It was revealed from the test of the hardened mortar that the SF-CF=75-25% (M3) specimen showed the highest compressive and flexural strength, and the SF-CF=50-50% (M6) specimen obtained the highest flexural toughness. Therefore, it was possible to confirm the synergistic reinforcement effect of that enhanced the strength and improved the flexural performance by hybrid of macro SF and micro CF. Based on the results of this experiment, the optimal mix proportion of SF-CF hybrid FRM is proposed in this paper to improve the compressive strength, flexural strength and flexural toughness.

Influence of Incinerated and Non-Incinerated waste paper on Properties of Cement Mortar

The cement industry is one of the most polluting industries globally, due to the high amount of CO2 emissions generated during production. Improving the sustainability of cement production is thus vital. Waste paper is also a big problem for many societies, especially in developed countries, where the use of board and paper increases almost every day. This work examines the possibility of using incinerated waste paper ash (IWPA) and non-incinerated waste paper (NIWP) as a partial replacement for cement (by weight) in mortar mixtures. For non-incinerated waste paper, the tested replacement levels were 1%, 1.5%, 2.5% and 3.5%, while for incinerated waste paper, the replacement levels were 2.5%, 5%, 7.5%, and 10%. An additional mix without any replacement was also cast for comparison purposes. The fresh and hardened properties of mortar were assessed using flow rate, compressive strength, direct tensile strength, water absorption, and dry density tests, and two test ages (7 and 28 days) were considered for the compressive and tensile strength tests, though water absorption and density tests were undertaken at 28 days only. The results showed that the presence of waste paper (incinerated or non-incinerated) reduced the flow rate of fresh mortar as compared with the reference mix. It was also found that, for the NIWP mixtures, 1% replacement of cement was the most efficient percentage; this increased the compressive strength by 16% and the direct tensile strength by 19% at 28 days of age. For the IWPA mixes, the results showed that the best replacement ratio was 5%, where the compressive strength and direct tensile strength were improved by 10% and 11% at 28 days, respectively. These 1% NIWP and 5% IWPA mixtures gave similar water absorption of 7% to the reference mix.

Effect of Air-Entrained Agent on Fresh and Hardened Properties of Cement Mortar

Freezing and thawing action is the main cause of the deterioration of the reinforced concrete structures. It decreases its durability if appropriate precaution is not taken into account. In order to minimize the effect of freezing and thawing action, generally 4∼7 % of air content by volume of concrete is introduced into the concrete. Air content in the concrete is considered as the combination of the entrapped air and entrained air. Entrapped air is minimized as less as possible during the compaction process of concrete and instead, the microscopic air cells are entrained into the concrete by using air entrained agent during the mixing. This paper is focused on the content of highly effective air-entrained agent (AE 303A), on the fresh and hardened cement mortar. The air content of mortar was increased from 2.7% to 10.5% while using 0.01% of AE 303A by weight of cement. The density of fresh mortar was decreased from 2.261 g/cm 3 to 2.078 g/cm 3 and that of hardened mortar was from 2.238 g/cm 3 to 2.039 g/cm 3 . With similar trend of decreasing densities, seven days compressive strength was decreased from 43.12 MPa to 27.37 MPa. However, no significant difference was observed on the workability of mortar, measured in table flow value while increasing the AE 303A content.

Mechanical and perceptual characterization of ultra-high-performance cement-based composites with silane-treated graphene nano-platelets

An ultra-high-performance cement-based composite (UHPCC) with excellent mechanical behaviors and self-perceived properties was successfully prepared in this work. The effects of silane-treated graphene nano-platelets (ST-GNPs) on the fluidity, porosity, degree of hydration, mechanical behaviors, and self-perceived properties of UHPCC were investigated. The results revealed that the fluidity of UHPCC fresh mortar is directly related to ST-GNPs content. The fluidity decreases as the amount of ST-GNPs increases. Furthermore, when the amount of ST-GNPs was 0.05%, the porosity of UHPCC was found to be 11.5%, and the compressive strength and flexural strength reached the maximum value of 142.5 MPa and 23.8 MPa, respectively. Additionally, the microstructure of the UHPCC was investigated. Also, it was indicated that the introduction of ST-GNPs could enhance the transformation of fibrous calcium silicate hydrate (C–S–H) gel into petal-like hydration products, which has the tendency to continuous interpenetration. Further, the introduction of ST-GNPs is confirmed to reduce the resistivity of UHPCC from 18.85 kΩ·m to 6.26 kΩ·m. Finally, the self-perceived performance of UHPCC with 0.05% ST-GNPs was observed to be about double that of UHPCC without ST-GNPs, which indicates that the UHPCC prepared by adding ST-GNPs has excellent self-perceived performance.

Utilization potential of aerated concrete block powder and clay brick powder from C&D waste

This paper intends to study the recycled powder generated from aerated concrete blocks and sintered clay bricks. The powder was divided into different groups according to particle sizes with ranges of 0–0.045 mm, 0.045–0.075 mm and 0.075–0.15 mm. First, the energy consumption to prepare the powder with different particle sizes was calculated according to the grinding time. Various groups of powder were used to cast mortar samples with cement replacements of 10%, 20% and 30%. The slump and slump loss of the fresh mortar and the mechanical properties of the hardened mortar after 28 days of curing were investigated, as well as the shrinkage within 60 days. The results show that aerated concrete blocks are easier to crush than sintered clay bricks, but the energy consumption of grinding aerated concrete blocks into powder finer than 0.30 mm is higher than that of grinding sintered clay brick powder, which is verified by the energy consumption analysis. The mortar strength can be improved by replacing 10% cement with the recycled powder. The activities of three kinds of powder, from fine to coarse, obtained from aerated concrete blocks are 98.4%, 83.6% and 74.6%. For sintered clay brick powder, the activities are 73.7%, 87.9% and 85.8%. The aerated concrete block powder particles contain 2–3 μm pores, which is the reason that it severely reduces the fluidity of the mortar, leading to considerably more shrinkage.

Rheological, mechanical, and abrasion characteristics of polymer-modified cement mortar and concrete

The settlement of fresh concrete or improper operation during construction usually makes the water to cement (w/c) ratio of the cement mortar on the concrete pavement surface higher than designed, which may influence the abrasion resistance of concrete pavement. This study firstly tried to establish relationships between abrasion of hardened cement mortar and rheological characteristics of fresh cement mortar in the laboratory. Secondly, a polymer-modified cement mortar was developed with carboxyl styrene butadiene rubber latex added to the cement mortar. Its rheological properties in mixing, mechanical properties, and abrasion were investigated. It is found that the polymer-modified cement mortar has a much better abrasion resistance and flexural strength while lower compressive strength than cement mortar. A stronger correlation was observed between flexural strength rather than compressive strength and abrasion resistance of cement mortar. The proposed polymer-modified concrete also exhibited good abrasion resistance.

Effectiveness of air entraining agent and defoamer on the bubble distribution of fresh mortar under different mixing methods

The purpose of this study was to elucidate the distribution of fine bubbles and coarse bubbles in the mortar system of cement-superfine slag powder mortar after multiple mixing of air-entraining agent and defoaming agent. The experimental study used a fresh concrete pore structure analyzer (AVA instrument) to measure the bubble size distribution and related bubble parameters of fresh mortar. The critical size of the bubbles was defined as the size that the air bubbles can maintain the volume stability over time. Based on the time-dependent change in the volume content of the larger bubbles within two hours after mixing, it was found that 500 μm was the critical dimension of bubbles. By adjusting the mortar mixing methods, a lower mortar viscosity was achieved while the total volume of fine and coarse bubbles were also reduced. In addition, when the blending ratio of defoaming agent and air-entraining agent was within the range of 0.50-0.54, the bubble structure of the cement-superfine slag powder mortar had been significantly improved, and more fine bubbles and fewer coarse bubbles had been distributed in the mortar.

Monitoring the setting process of mortar by a simple mechanical test

ABSTRACTThe objective of this study was to investigate the feasibility of using a simple mechanical test to determine the setting time of mortar. The simple mechanical test was carried out on a cantilever PVC pipe filled with fresh mortar. The flexural strain response over time was monitored to investigate the setting process of mortar. The estimated setting time could be compared with that determined by the penetration resistance method. The experimental results show that the strain response of the PVC pipe and mortar can be divided into two stages. The first stage is that the cement mortar has not yet become plastic, and the flexural stress is mainly borne by the PVC pipe. The second stage is that the mortar has become plastic and gradually rigidified and has the ability to bear the flexural stress so that the strain of the PVC pipe decreases with time. Both the initial and final setting times of mortar obtained from the flexural test were in good agreement with those determined by the penetration resistance method. The proposed flexural test can be applied directly to measurement of the setting time of concrete without a need to remove the coarse aggregates larger than #4.

Development of a foam index test method by investigating the effect of test parameters

The foam index test is often performed to determine the air-entraining agent (AEA) dosage when fly ash is used in air-entrained concrete. However, hand-shaking and arbitrary chosen test parameters in the traditional test method lead to deviation between researches. In this paper, a horizontal shaker which can be easily obtained is used to provide automated agitation in a foam index test. The influence of shaking frequencies is investigated at first as the mode of shake is changed. Then, this research focuses on the influence of the water to cementitious materials ratio on foam index. By introducing a model paste consisting simulated pore solution and dead burnt MgO powder, several key factors are isolated. Analysis and discussion suggest that a prolonged shaking duration is more suitable for foam index tests. And by this prolonged method there exists good correlation between foam index and air-entraining agent dosages in fresh mortars.

Influence of Effective Water-to-Cement Ratios on Internal Damage and Salt Scaling of Concrete with Superabsorbent Polymer.

Superabsorbent polymer (SAP) is attracting attention as a water-entraining admixture that reduces shrinkage or heals cracks in concrete. Cross-linked sodium polyacrylate SAPs, which are the most widely produced SAPs in the global market, are applicable as concrete admixtures. However, there have been contradictory results on the freeze–thaw resistance of concrete with SAPs. This study aims to clarify these results considering the water absorption behavior of SAPs in hardened concrete when effective water-to-cement ratios are different. Firstly, the absorbencies of one kind of cross-linked sodium polyacrylate SAP (SAP_SP) in pore solution and fresh mortar were measured by a tea bag test and flow test, respectively. Pore size distribution, capillary water absorption, and deformation during freeze–thaw cycles were analyzed for mortar samples with varying SAP_SP dosages. In the main tests, concrete samples with three different SAP_SPs/cement ratios (0.1%, 0.2%, and 0.3%) and a reference sample were prepared, and internal damage and salt scaling were measured under freeze–thaw cycles. Because SAP_SP absorbs water in fresh mixtures, additional water was added to the mixture considering the water absorbency of the SAP_SP. It was found that the used SAP_SPs prematurely release their stored water so the effective water-to-cement ratio was increased when a larger amount of SAP_SP was used. The higher effective water-to-cement ratio caused more internal damage and salt scaling due to the weaker cementitious matrix. In addition, mortar samples with a high SAP_SP content show a larger absorption of capillary water than the reference sample. The result can be interpreted by an observation that SAP_SP in air voids absorbs water and expands to relatively large capillary pores or neighbor air voids during the capillary water absorption process.

Performance and ITZ of pervious concrete modified by vinyl acetate and ethylene copolymer dispersible powder

This work aimed to assess the influence of vinyl acetate and ethylene copolymer dispersible powder (VAE-P) on the performance and interfacial transition zone (ITZ) of pervious concrete, and explore the mechanism responsible for the resulted performance. Various pervious concretes and mortars were prepared, and the porosities, water permeability coefficients and strengths of pervious concretes were assessed, the fluidities, shear viscosities, air contents and strengths of various mortars were measured. The crystalline phase, pore characteristic and VAE-P layer in the ITZ were also investigated. The results indicate that VAE-P enhances fluidity and air content, and declines shear viscosity of fresh mortar. These pervious concretes with lower or similar porosity than the control still provide similar or better water permeability. It reduces mortar strength, but it significantly improves pervious concrete strengths. ITZ results indicate that it delays cement hydration, alters pore characteristic and especially increases the volume of pores with larger size. It increases VAE-P layer thickness. The pervious concrete with 10% VAE-P displays a cross-linked network layer structure. The pervious concrete with 5% VAE-P provides the lower strengths than that with 2.5% VAE-P, but pervious concretes with more VAE-P have relatively higher strengths. These results provide a reference for the preparation of pervious concrete with VAE-P.

Effects of metakaolin on properties and microstructure of magnesium phosphate cement

Metakaolin has been generally used as a filler in Portland cement-based materials, and it was proved to be able to enhance the performance of magnesium phosphate cement composites. In this research, metakaolin was introduced into MPC, and compressive strength, tensile bonding strength, porosity and durability of MPC were measured. The microstructure of MPC before and after water immersion was evaluated. The experimental results indicate that the presence of metakaolin can lead to higher plastic viscosity of fresh MPC mortar, 28-day compressive strength, higher tensile bonding strength, better freeze-thaw resistance, better water resistance, lower drying shrinkage and better optimized microstructure. Physical effects of metakaolin including filling effect and inducing effect play the leading role in MPC. Metakaolin particles can fill in the pores or cracks, resulting in the decrease in porosity. In addition, metakaolin particles can provide lots of sites for crystallization of hydration products, inducing in the generation of more homogeneous microstructure. Finally, the dissolution and chemical reaction of metakaolin particles were confirmed by BSE analysis.

On predictive modelling of yield stress increase in fresh cement paste

AbstractFreshly mixed concrete is composed of cement paste as fluid‐like component and aggregates as solid particulate component. Development of yield stress in fresh mortar is significant for reliable and high‐quality concrete operation as too low or too high yield stress causes process‐ability challenges like the multi‐layer problem, aggregate flocculation or blockage. Traditional experimental tests on the evolution of yield stress are costly since a wide spectrum of different material and environmental conditions needs to be studied. Progressing hydration, thermal effects and mechanical loading/unloading may influence spatial distribution of the apparent yield stress. However, this local information is very difficult to obtain using traditional laboratory tests and virtual fresh concrete testing is therefore promising.In the context of a single‐component flow approach to homogenized modelling of the cement paste composition at the macro‐scale, the microstructural evolution affecting the development and distribution of apparent yield stress is taken into account by a thermo‐chemo‐mechanical phase‐field model bridging the micro‐macro length scales by using a Ginzburg‐Landau‐type free energy function. The phase‐field, that describes the smooth spatial transition between fluid‐like and solid‐like behaviour of cement paste in the setting phase, is governed by bond‐building chemical processes (hydration) and reversely‐acting mechanical effects (bond breakup). The resulting set of coupled nonlinear advection‐reaction‐diffusion equations are formulated in the Eulerian framework and discretized in space using the weighted residuals method and finite differences in time. Implementation of the predictive model is demonstrated using the FEniCS framework, together with numerical examples supporting model validation.

A new test method to characterize the pressure-dependent shear behavior of fresh concrete

The development of formwork pressure is essentially affected by the rheological behavior of fresh concrete, while the shear behavior itself might be influenced by the magnitude of normal pressure. A test set-up was developed in which the fresh mortar and concrete can be sheared in a pressure cell by a vane as a part of a concrete rheometer (ICAR). The concrete is directly loaded in the pressure cell by a hydraulic jack. Preliminary shear tests were conducted on concretes with moderate and high flowability at constant water/binder-ratio of 0.4 with the focus on the static yield stress. The additional pressure was applied up to 240 kPa. The consistency class of the concrete F4, F5 and F6 was varied by choosing the paste volume to 300, 315 and 330 l/m3, respectively. The results show the significant influence of applied pressure on the measured yield torque or yield stress in early concrete age especially for concretes with moderate flowability (F4) or with relatively high volume fraction of aggregates respectively. However, a significant increase of yield resistance by applied pressure was identified for all concretes after 90 min concrete age.

Reuse of Waste Material “Waste Sludge Water” from a Concrete Plant in Cement Composites: A Case Study

This paper presents the results of research dealing with the use of recycled waste sludge water from a concrete plant (CP) as partial or complete replacement of mixing water in cement mixtures. The need to recycle waste sludge water generated as a by-product (waste sludge water) during the production of fresh concrete in the concrete plant results from the environmental and economic problems associated with the operation of the concrete plant. Mixing water was replaced with recycled waste sludge water in the amount of 25%, 50%, 75%, and 100%. In order to determine the effect of partial or complete replacement of mixing water with waste sludge water from the concrete plant in the production of cement composites, laboratory tests of waste sludge water were carried out to determine whether the waste sludge water complies with the requirements for mixing water defined in CSN EN 1008. The tests also determined the properties of fresh cement mortar and hardened cement composites. These were tests of the beginning and end of cement mortar setting, and the strength characteristics (flexural strength, compressive strength). The results of these tests show that it is possible to replace the mixing water by waste sludge water from the concrete plant in the amount of up to 25% without significantly affecting the tested properties, in comparison with the formula containing pure mixing water.

Effects of hydroxyethyl methyl cellulose ether on the hydration and compressive strength of calcium aluminate cement

Aluminate containing phases such as tricalcium aluminate (C3A) and dodecacalcium heptaaluminate (C12A7) play a key role in the reaction between Portland cement and cellulose ether. In order to simplify such impact from calcium aluminate, calcium aluminate cement (CAC) was applied as a carrier. Effects of hydroxyethyl methyl cellulose ether (HEMC) on the hydration of CAC were characterized by means of isothermal calorimetry, X-ray diffraction analysis, thermal analysis and scanning electron microscopy, respectively. Meanwhile, the setting times, water retention, air content and compressive strengths of HEMC modified CAC pastes or mortars were also determined. Results indicate that HEMC prominently delays the hydration of CAC within 1 day, and the higher dosage of HEMC, the longer setting times. HEMC exerts no obvious impact on the formation amount of CAH10, only leads to a smaller crystal size. From aspect of physical and mechanical properties, the addition of HEMC improves the water retention of fresh CAC mortars, and only with addition of 0.1% HEMC, the water retention of fresh CAC mortars almost approaches 100%. Additionally, the addition of HEMC also significantly promotes the air content of fresh CAC mortars, leading to an obvious decrease in the compressive strengths.

Experimental research on magnesium phosphate cements modified by red mud

The main concern of this article is to understand the influences of red mud on the properties of magnesium phosphate cement (MPC), which were determined in terms of the fluidity, setting characteristic, temperature evolution during the hardening stage, mechanical properties, water resistance, hydration products, pore structure and microstructure. The results showed that the fluidity can increase to a value of 272.5 mm at a level of 20% red mud, and red mud was found to decrease the exothermic reaction intensity of the fresh mortar and to prolong the setting time to 25 min during the hardening stage. The mortar prepared with suitable addition of red mud presented with improved mechanical properties and enhanced water resistance during the whole ageing period, and the group containing 20% red mud yielded the highest compressive strength of 90.2 MPa at 28 days. Then, the pore structure was measured by low-field nuclear magnetic resonance (LF-NMR), which was found that adding red mud can reduce the total porosity and form more small pores. Moreover, the microstructure and the hydration products of the samples were tested by X-ray diffraction (XRD), scanning electron microscopy (SEM) along with energy dispersive spectrometer (EDS). The obtained results illustrated that red mud can fill in the microcracks, making the structure denser, and also formed with some new hydrates. The present work aimed at the utilization of red mud and the results illustrated that MPC can be modified by red mud significantly.

The effect of open-air curing on compressive strength of geopolymer mortar containing laterite soil and slaked lime

Most surface layers in the Papua and Kalimantan regions are Laterite Land. When dry lateritic soil dries but when containing large amounts of water, laterite soil becomes overtime. Cement production requires a lot of energy so that geopolymer concrete and mortar is a material that has great potential as an alternative to reduce the use of Portland cement because it has mechanical properties that almost resemble Portland cement-based concrete. This study discusses the use of fly ash and alkali activator (NaOH and Na2SiO3) to bind laterite soil by adding quenched lime to reduce the use of ovens to form geopolymer mortar. Comparison of laterite and lime outages is used, namely 95%: 5% and 90%: 10%. Testing of the flow of fresh geopolymer mortar shows that all materials can be bonded well and no segregation occurs. The hardened test material is treated in air-exposed for 3, 7 and 28 days. Testing of compressive strength was analyzed to determine the behavior of geopolymer mortar. The test results showed that there was an increase in compressive strength from the age of 3 to 7 days but decreased at the age of 28 days due to rainy weather, sunlight which resulted in the specimen experiencing flowers (during rain) and shrinkage (during hot weather) so that cracks occurred cracks in specimens, as well as the use of comparison of laterite and lime soils, extinguished 90%: 10% resulting in better compressive strength compared to the use of the ratio of laterite and lime outages of 95%: 5%.