Mortar Setting Research Articles

Influence of Aluminous Cement on the Hardening Rate of Cement-Based Stucco Mortars

Renovation mortars used to restore damaged stucco elements are materials with special physical properties due to the nature of the work and environment in which they are applied. They must be characterized by low shrinkage, relatively short setting time, appropriate working properties and hydrophobic nature of hardened mortar. This paper analyzes the impact of mortar stucco ingredients on these parameters. The analysis was performed by experimental studies. The effect of the content ratio of aluminate cement to Portland cement on the change in mortar setting time was studied. Suitable workability of fresh mortar is achieved by the use of consistence-modifying additives. To assess this parameter, flow table method was applied in accordance with PN-EN 1015-3: 2000. The additives used were a system of thickeners, which included: cellulose ether in the form of hydroxyethylmethylcellulose and modified starch ether (starch 2-hydroxypropyl ether). Hydrophobic properties were obtained by the addition of triethoxyoctylsilane. The results were presented as graphs and tables. It was found that the ratio of aluminous cement to Portland cement most beneficial in terms of the setting rate of the resulting stucco mortar is 25% (m/m). This amount accelerates the end of setting time to 2 hours, the beginning of the setting time being 20 minutes. Suitable working characteristics were obtained by the addition of 0.080% of hydroxyethylmethylcellulose and 0.025% (m/m in dry mix) of starch 2-hydroxypropyl ether. Best hydrophobic properties of the hardened mortar was obtained by the addition of 0.075% (m/m in dry mix) of triethoxyoctylsilane.

Testing the Setting and Hardening of Concrete Using the Prism Technique

In non-destructive testing of concrete, the ultrasonic pulse-echo technique has proven to be a reliable method for locating cracks and other internal defects. An electro-mechanical transducer is used to generate a short pulse of ultrasonic stress waves that propagate into the object being inspected. Reflection of the stress pulse occurs at boundaries separating materials with different densities and elastic properties. The reflected pulse travels back to the transducer that also acts as a receiver. The received signal can give many insights to the properties of materials under test.The question arises how the setting and hardening of cement paste, mortar, and concrete can be measured continuously. Continuous measurement ask sfor non destructive methods. The current testing method such as the vicat needle for cement paste and penetration resistance test for concrete methods measure at intervals.These methods can be applied before the end of setting. All these methods do not allow continuous measurements and are partly destructive. In this paper a special pulse-echo technique called prism technique is used to evaluate the evolution of proprieties of concrete over time. For that, an automatic system has been developed with labview program in order to monitor the time of flight of the reflected p-wave. Two mixtures of mortar are made using different proportions, of water, cement, and sand. The mortar is poured into a mould that has a form of a prism. Measurements are taken every 10 minutes over a period of 24 hours. This enabled us to plot the evolution of p-wave velocities over time for the samples and compare the results.

Testing phosphate ions as corrosion inhibitors for construction steel in mortars

The purpose of this investigation is to analyze the effectiveness of phosphates as inhibiting agents for steel bars embedded in mortars. Three mix designs were selected for this study: mix A had no admixed chlorides and was used as reference; mix designs B and C were contaminated with 1% in weight of chlorides/weight of cement and mix C also incorporated 7% Na3PO4.12H2O. After setting for 48h, the samples were cured for 7 days immersed in water. Three specimens of each group were then immersed in aerated saline solutions 0.5molL−1 NaCl during 720 days. The corrosion potential (Ecorr), the polarization resistance (Rp) and the electrochemical impedance spectra were recorded regularly. After 720 days of immersion one set of mortars was anodically polarized and another set cathodically polarized. After that, Raman spectra of corrosion products were registered. Additional specimens were used to evaluate porosity and chloride profiles. The presence of phosphate ions as inhibitors has no effect on Ecorr values and suggests mixed-type inhibition. Mix C remains passive until 180 days of exposure, with Rt>100kΩcm2. At longer times, Rt decreases in time but the inhibition percentage is always higher than 95% when evaluated by impedance spectra. Using Rp, inhibition stays above 70%. Anodic and cathodic polarization curves, together with corrosion potential values, suggest that phosphates behave as a mixed-type inhibitor.

Using First-Person Perspective Filming Techniques for a Chemistry Laboratory Demonstration To Facilitate a Flipped Pre-Lab

The current model of flipped classroom ensures that learning is not being restricted to the brick and mortar setting. Lessons can be conducted anywhere, anytime, as long as there is a good internet connection. Most of the flipped classroom and e-lectures are videos recording PowerPoint slides with a human voice as the audio instruction. In laboratory teaching, flipped pre-lab is not typical. The closest it gets is the filming of laboratory demonstration using a handheld camcorder. How can we captivate the audience in a manner that will make it an even more realistic demonstration? The application of a small device, GoPro camera, empowers the demonstrator to teach his students with a new perspective.

Screening of bacteria and concrete compatible protection materials

Bacteria that can induce calcium carbonate precipitation have been studied for self-healing concrete applications. Due to the harsh environment of concrete, i.e. very high pH, small pore size and dry conditions, protection methods/materials have been used to preserve the bacterial agents. A wide screening of commercially available materials is thus required to evaluate them as alternatives. This study describes the influence of six commercially available possible protection approaches (diatomaceous earth, metakaolin, expanded clay, granular activated carbon, zeolite and air entrainment) on mortar setting and compressive strength when combined with either Bacillus sphaericus spores or Diaphorobacter nitroreducens and their respective nutrients. The influence of two novel, self-protected, bacterial agents was also investigated within the same scope. The most severe effect on setting time was observed as an undesirable delay of 340min in all samples containing nutrients for ureolytic bacteria. Samples containing B.sphaericus spores showed the most significant decreases in compressive strength up to 68%. Yet, the addition of either D.nitroreducens or its respective nutrients did not cause major impact on both the setting times and the compressive strengths of the mortar specimens. The latter thus appears to be a suitable bacterial agent for further research on self-healing concrete. Likewise, the use of the novel self-protected bacterial agents did not affect the setting and the compressive strength of mortar. These results pave the way to replace protection materials with self-protection techniques. The latter should be further investigated for development of microbial self-healing concrete.

Estimation of mortars compressive strength at different curing temperature by the maturity method

Two set of mortars were made with three mineral additions to verify the relationship between compressive strength and maturity at later age. One cured in steam room at constant temperature of 20, 30, 40 and 50°C and the second cured under variable temperature history. It was found that a limited maturity index of 350°C days exists beyond which the relationship between strength and maturity is not unique. The newly proposed maturity index allows a better correlation between strength and maturity at later age and takes into consideration the deterioration of microstructure with temperature rise. Later age strength can be predicted using the relationship strength-maturity at early age with a correlation coefficient ranging from 0.89 to 0.98.

Influence of clay minerals addition on mechanical properties of air lime–metakaolin mortars

Two sets of mortars differing in type of lime and metakaolin, with air lime:sand volumetric ratio 1:3 were prepared with the aim to be used for restoration of historic masonries. The first set involved air lime and 20wt.% of metakaolin with more impurities (calcite and kaolinite, respectively) and with higher bulk densities compared to materials from the second set. Clay minerals (sepiolite, zeolite A, palygorskite and vermiculite) characterised by high specific surface areas and thus able to keep water in the structure and promote pozzolanic activity of metakaolins were used as additives in air lime and air lime–metakaolin mortars and their impact was evaluated in a view of mechanical strength at 28, 90 and 180days. Substitution of air lime from the first set by clay mineral and/or metakaolin caused improvement of mechanical strengths predominantly at latter ages, while lime mortars from second set suffer by lack of binder when other additives are supplemented and just palygorskite incorporation improves flexural strength, while vermiculite and metakaolin create mixture with improved compressive strength than lime mortar alone.

Characterisation of a new protocol for mortar dating: 14C evidences

Mortars represent a class of material basically constituted by a mixture of different phases (<em>i.e.</em> binder, aggregates, water) and widespread used for constructive uses and artworks. Current scientific literature regarding the possibility of mortar radiocarbon dating reports different and still contradictory results. Most of the observed inaccuracy of the dating method often derives from the presence of carbonaceous residuals of limestone origins drastically increasing the mortar age estimation contributing with significant aliquots of dead carbon. Most of the existing methodologies aim to isolate binder from other materials, preserving a trace of the 14C signature of the atmosphere absorbed during mortar setting. In this work a series of measurements (i.e. %C and 14C) of different matrices involved in the mortar production process simulated in a simplified version in the laboratory environment will be shown. More in detail the isotopic signature of the CO2 present in the laboratory air during mortar setting is compared with the signal extracted from the synthesised mortar by means of a separation protocol of the binder. Our analyses are performed with the aim to evaluate this procedure of dead C suppression efficiency for accurate mortar radiocarbon dating.

モルタルの凝結に銅化合物および亜鉛化合物が与える影響

本研究では、塩基性炭酸銅、酸化銅（Ⅰ）、酸化銅（Ⅱ）および硫酸銅（Ⅱ）五水和物の4種類の銅化合物と、酸化亜鉛、硝酸亜鉛六水和物、塩基性炭酸亜鉛および硫化亜鉛の4種類の亜鉛化合物を用い、これらがモルタルの凝結特性に与える影響を検討した。その結果、同じ金属であっても塩の種類によって凝結遅延作用が異なること、塩基性炭酸銅と酸化亜鉛の凝結遅延作用が大きいことが分かった。また、塩基性炭酸銅と酸化亜鉛を併用することで、凝結の始発が最大で20日まで遅延することを示した。

정제화 방법을 이용한 응결 지연제의 특성에 관한 연구

When hot weather concrete is utilized, the cooling methods of cooling pipe, liquid nitrogen, ice, etc., are used to prevent the poor consistency and cold joint due to high temperature. These methods, however, spike the production cost and energy consumption, and make quality control difficult. Among these methods is one that involves the use of a retarder. Although economical, retarder is caused difficulty of retarded hardening and setting time control due to inaccurate weighing and poor working condition. Therefore, how to make a tablet for hot weather concrete, as with the existing pharmacy and foods, is discussed in this study, including the following items: mortar setting time, flow test by elapsed time, physical and mechanical properties of concrete. As a result, gluconic acid is superior to lignosulfonic acid and the possibility of using them for such purpose without quality degradation was confirmed in this study, when retarder is tabletting.

Influence of the Mineralogical and Mortar Components on the Adherence of Some “Granites”

Rock plate setting can be performed with metal inserts or by mortar adhesion. For mortar setting, the adhesion bond strength values, as a rule, should be above 1 MPa. In the present work, tests with eight types of “granite” tiles were performed to compare the adherence of five types of mortars. The rocks chosen were: Red Brasilia (syenogranite), Black Indian (migmatite), Green Labrador (charnockite), Black Sao Gabriel (hypersthene diorite), Rose Jacaranda (nebulitic migmatite syenogranite), Fantastic Blue (biotite monzogranite megaporphyritic serial gneissified), Grey Swallow (monzogranite) and Yellow Ornamental (garnet porphyroblastic gneiss), which do not have similar petrographic and sawability characteristics, thereby resulting in different initial roughness values of the plates obtained by breaking apart the blocks on the gangsaw machine, which use granulated steel as an abrasive element. The adherence of these rocks with the mortars was determined in the rough surface as well as in the polished surface by the pullout traction test, standardized for ceramics. The results showed that the mortar adhesion is related to roughness, to mineralogy and to the texture of these rocks. To verify this relationship, tensile bond strength tests were performed with the main mineral components of these rocks using single crystals with known optical orientation. Moreover, the microstructure study of the standard substrate/mortar/rock set was also performed.

Use of tabletting & coating accelerator for the prevention of early-frost of concrete in cold weather

Abstract The use of accelerators prevents early-frost by developing strength of concrete in cold weather. However, no security of workability occurs because early hydration makes them to react rapidly. Thus, the accelerators via tabletting were coated with polyvinyl alcohol (PVA) of water-soluble polymer substance. The discussion includes the following: mortar setting time, workability by elapsed time, early strength to assure the development of adequate strength, and freezing–thawing resistance. As a result, workability can be secured as well as the development of early strength to prevent early-frost. The porosity and progress of hydration affecting the concrete were also found to be superior by analyzing the mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) results.

Monitoring the Air Influence on Cement–Lime Mortar Hydration Using Low-Field Nuclear Magnetic Resonance Relaxometry

In the present study, we investigate the relationship between the nuclear magnetic resonance relaxation rate and the hydration time in two types of masonry cement-lime mortar. The studies are performed with the mortars both in an enclosed and a standard atmosphere to monitor the air influence on cement-lime mortar hydration and setting. The constituents of the investigated mortar samples are: cement, slaked lime, sand and water. They were mixed to achieve a flow spread of 10 cm. These types of mortars are usually suitable for historical masonry maintenance, but they can also be used for modern buildings, or even for concrete structures coatings to prevent concrete carbonation. All nuclear magnetic resonance relaxation experiments were performed at 20 °C using a low-field nuclear magnetic resonance instrument operable at 20 MHz proton resonance frequency. A slowing down of the hydration kinetics is demonstrated for the samples kept in closed atmosphere conditions. The results contribute to the understanding of cement–lime mortar hydration, carbonation and setting under closed atmosphere conditions.

Decalcification of cement mortars: Characterisation and modelling

Abstract This paper presents the results of a thorough microstructural characterisation of a set of cement mortars (made with three w/b ratios and five different cement types), degraded by the ammonium nitrate method. Both destructive and ultrasonic non-destructive techniques were used to characterise the samples. The initial calcium content of the samples plays a dominant role in both the advance of the degradation process and the degradation grade of the samples. In addition, the decalcification process kinetics and the degradation grade are modelled, using Fick’s second law of diffusion and the shrinking unreacted-core model. Two parametric equations are presented and used to estimate the decalcification process kinetics and the degradation grade using accessible microstructural parameters of the native mortars, such as the initial CaO content, the open porosity, and the cementitious matrix volume fraction. Furthermore, the degraded depth in the samples is measured using ultrasonic testing with an average error of about 10%.

Cyclic behaviour of a lightweight mortar with cork granulate composite

This paper presents an experimental analysis of the cyclical behaviour of a novel composite material made from a traditional mortar with incorporation of granulated cork. This material is hereby designated by CorBe. Specimens with 0%, 15% and 30% of cork addition, in volume of the mixture, were prepared and tested. Four types of cork with different cork grain sizes were used on each volume fraction. In order to characterise the cyclical behaviour of this composite material, cyclic uniaxial and diagonal compression tests were carried out. The energy dissipation capacity of these mortars was also studied. Obtained results evidenced that, for the whole set of mortars studied, there is a clear tendency for the improvement of performance when cork granulates are added, either for cyclic uniaxial or for diagonal compression loadings. The overall results prove the advantages of the application of CorBe in structural elements aimed for energy dissipation. Furthermore, the rupture mechanisms under cyclical loadings of this composite material were also analysed and discussed.

Effect of Fly Ash Fineness on Temperature Rise, Setting, and Strength Development of Mortar

AbstractThis paper investigates the effects of the fineness and replacement ratio of fly ash on the temperature rise and setting time, and compressive, tensile, and flexural strength of mortar mixtures. Three types of fly ash with Blaine finenesses of 4,125 cm2/g (40F), 6,686 cm2/g (60F), and 9,632 cm2/g (90F) were used to replace Portland cement at replacement ratios of 0 (which was the control mix), 15, 30, 45, and 60% by binder mass. Test results demonstrate that using fly ash as a cement replacement resulted in a reduction in the maximum temperature rise in mortar regardless of the fineness of the fly ash. In this investigation, 15 fly ash replacement caused a reduction in the peak temperature of about 4 to 6°C in the mortar. The setting time of fly ash mixes where 15 and 30% of the cement was replaced with fine fly ashes was faster than that of the control mix. The compressive strength of mortar mixes using finer fly ashes (60F and 90F) was significantly improved compared to that of the 40F fly as...

Characterization of cement-based materials using a reusable piezoelectric impedance-basedsensor

This paper proposes a reusable sensor, which employs a piezoceramic (PZT) plate as anactive sensing transducer, for non-destructive monitoring of cement-based materials basedon the electromechanical impedance (EMI) sensing technique. The advantage ofthe sensor design is that the PZT can be easily removed from the set-up andre-used for repetitive tests. The applicability of the sensor was demonstrated formonitoring of the setting of cement mortar. EMI measurements were performedusing an impedance analyzer and the transformation of the specimen from theplastic to solid state was monitored by automatically measuring the changes in thePZT conductance spectra with respect to curing time using the root mean squaredeviation (RMSD) algorithm. In another experiment, drying-induced moisture lossof a hardened mortar specimen at saturated surface dry (SSD) condition wasmeasured, and monitored using the reusable sensor to establish a correlationbetween the RMSD values and moisture loss rate. The reusable sensor was alsodemonstrated for detecting progressive damages imparted on a mortar specimen attachedwith the sensor under several loading levels before allowing it to load to failure.Overall, the reusable sensor is an effective and efficient monitoring device that couldpossibly be used for field application in characterization of cement-based materials.

Air Lime Mortars: The Influence of Calcareous Aggregate and Filler Addition

Many historical buildings with renders based in air lime still exist in Portugal. These old mortars have proved to be durable and reliable materials. However, new lime mortars prepared nowadays to be used in conservation practice, often present low strength in comparison with cement mortars. This paper presents a study of the viability of improving the performance of lime mortars through the use of different nature aggregates (Tagus River siliceous sand and crushed calcareous sand) as well as different size distributions, varying the filler contents. For that purpose a set of mortars with volumetric proportion of 1:3 (lime:aggregate), using siliceous sand from Tagus river or calcareous sand and including different volume percentages of aggregate replacement by filler (0% of incorporation, 5% of incorporation, 10% of incorporation), were prepared. An evaluation of the main characteristics of this set of mortars was made in terms of: i) hygric behaviour (water absorption by capillarity), and ii) mechanical resistance (flexural and compressive strength and elastic modulus). This study aims to assess the viability and possible advantages of using calcareous aggregate in lime mortars and to evaluate the possibility of improving characteristics through a better compaction obtained by the incorporation of different ratios of filler.

Résistance à la traction et module d’élasticité des bétons calcaires: application à des mélanges tunisiens

This article presents the results of the tensile strength and the elastic modulus obtained between one day and a year on a vast set of mortars, micro-concretes and concretes carried out with limestone aggregates out coming from five Tunisian careers. For the tensile strength, the results were compared with the compression strength measured on the same mixtures. The obtained evolutions do not coincide with the power-laws generally adopted for the predicted tensile strength. An approach, where the law parameters (coefficient, exponent) can be adjusted, gives better results. The resort to another more precise model, described by a hyperbolic law, makes it possible to provide a physical interpretation to the tensile strength behavior of the hydraulic mixtures. Its parameters are linked to the aggregate strength and cohesion in the paste-aggregate transition zone. For the elastic modulus, the use of a model taking into account the properties of the granular phase and the binding phase made it possible to reach the elastic modulus of the aggregates.

Monitoring the setting and hardening of early-age mortar using a pulse-echo ultrasonic guided wave approach

A pulse-echo ultrasonic guided wave approach that monitors the setting and hardening of early-age mortar during the first twenty-four hours ofhydration is presented. The method transmits a torsional wave mode on one end of a cylindrical steel rod embedded in mortar and then receives the reflected signals. Both the reflection from the end of the rod and the reflection from the point where the waveguide enters the mortar are monitored. The development of the mortar's mechanical properties is related to both the energy leaked into the surrounding mortar and the energy reflected at the entry point. Experiments were performed on mixtures with varying water-cement ratios (w/c = 0.40, 0.50, and 0.60), chemical admixtures (accelerant and retardant), and mineral admixtures (silica fume and fly ash). The time of setting and compressive strength of the different mortar mixtures was determined in accordance with ASTM standards. The change in signal strength of the end- and entry-reflection of the guided wave appears to be correlated to the setting times and compressive strength of the mortar. The ability of this method to only require access to one side of the specimen makes it attractive for the development of a portable system that monitors early-age cementitious materials in the field.