Fresh Mortar Research Articles

Mechanical properties and deformation behaviour of early age concrete in the context of digital construction

Digital construction is gradually opening unlimited possibilities for building and concrete industry. The key secret for a robust print process lies in our understanding of the processing technology and material fresh properties, in addition to developing novel measurement and control techniques. This paper aims to gain a better understanding of early age mechanical properties of 3D printable materials and improve it for the requirement of large scale concrete printing. Experimental investigations were carried out to measure green strength and stiffness of fresh fly ash-cement mortar with applied 3D optical metrology. The compressive green strength was linked with material yield strength evolution and later, modified with nanoclay for higher buildability properties. Nanoclay addition deceased the layer deformation due to significant increase in Young's modulus and to estimate this uncontrolled deformation, a mathematical function was formulated, which subsequently validated by comparison to printing experiments.

The influence of the ageing of calcium aluminate cement on the properties of mortar

This paper presents an on-going study of the influence of the ageing of calcium aluminate cement (CAC) and its mixtures with additives on the properties of fresh and hardened mortar without any deflocculants. DTA, TG, XRD, and SEM methods for hardening products and structure analysis and as well methods for evaluation technical characteristics of mortar, such as the flowability, compressive strength, density, and ultrasonic wave propagation velocity, were used in the work. The results revealed that the ageing of the raw materials in a climatic chamber at 95% relative humidity (RH) and 20 ± 1 °C for 7 days caused a decrease in the flowability of fresh mortar. This characteristic was also influenced by the properties of the additives. The mortar prepared from 14-days-aged raw materials was not flowable. The overall weight loss upon heating and the XRD data indicated a significant increase in the hydration products formed during mortar hardening when the ageing time of the raw materials was extended from 7 to 14 days compared to the amount of hydration products in the hardened mortar prepared from 7-days-aged raw materials. This increase is probably due to the peeling of the carbonated hydration products of cement particles, formed during ageing for 7 days, from the surface when the ageing time is prolonged beyond 7 days, leading to an increased hydration of the cement particles. The ageing of the raw materials has a negative effect on the compressive strength and density of hardened mortar. The formation of hydration products during mortar hardening and the compressive strength and density are affected by the properties of the additives.

Comparison of Efficiency of Accelerating Admixtures for Concrete Using Multiple-Criteria Decision Analysis (MCDA)

A lot of different types of accelerating admixtures for concrete are used nowadays. The aim of this paper is to determine efficiency relations between several accelerating admixtures for concrete with usage of multiple-criteria decision analysis (MCDA). Tests of cements’ initial setting time, consistency and compressive strength of mortars were made. Tests of cements and fresh mortars were conducted in temperature 8°C and 20°C. Compressive strength were tested after 12, 24, 48 hours and 7, 28 days of curing. Specimens for those tests were cured in temperature 8°C in water and 20°C in climatic chamber with relative humidity 60%. Mortars were made of Portland cement (CEM I 52,5R), Portland-slag cement (CEM II/B-S) and two kinds of blast furnace cement (CEM III/A, CEM III/C). Examined admixtures were based on calcium formate, crystal seeds and calcium nitrate. All of them are described as both set and hardening accelerators for concrete. Admixtures were added in maximum dosage allowed by producer. All of admixtures caused decrease of initial setting time and increase of early compressive strength (12-48 hours) with varying degrees. Decrease of 28 days compressive strength was not noted in case of any admixture. In order to determination of efficiency relations the multiple-criteria decision analysis (MCDA) was made for every kind of cement separately. Criteria were defined on the basis of conducted tests and were divided accordingly to environmental conditions. Weights of criteria were evaluated with pair analysis method. Values of tests’ results were converted with usage of Neuman-Morgenstern method. Result of analysis is sum of criteria evaluations according to their weights. Accelerating admixture based on crystal seeds in proven to be the most efficient one, while the one based on calcium formate is the least efficient of tested admixtures.

Relationship Between Air-Content in Fresh Cement Paste, Mortar, Mix and Hardened Concrete Acc. to PN-EN 480-1 with Air-Entraining CEM II/B-V

Research results of the relationships between air-volume in air-entrained cement paste, mortar and concrete, all designed according to PN-EN 480-1 guidelines are presented in the paper. The cement paste, mortar and concrete, with w/c=0,5 ratio, were prepared using innovative air-entraining cement CEM II/B-V. The air-entraining cement CEM II/B-V was produced using two methods: mixed together with natural or synthetic aerated admixture. The air volume test of the volumetric method was carried out in case of fresh cement paste, mortar and concrete mix. Fresh concretes were evaluated in terms of stability of air entrainment and consistency for 5, 20 and 40 min. The porosity structure parameters, like summarized air-content, specific surface of air voids, air-voids spacing factor and micropores content of hardened concrete, were estimated using computer tomography with a resolution of 2-5 μm. The aim of the research was to determine the dependence between air-content of cement paste, mortar and concrete on the measurement of air-entrainment of cement paste or mortar with the same w/c ratio and type of cement, all designed according to PN-EN 480-1 guidelines. Test results proved that there is a good correlation between the measured air-content of the cement paste, mortar and concrete. Therefore, it is possible to predict the aeration of concrete on the air-entrainment of the mortar. Moreover, the porosity parameters research results indicated, that the air-entrainment of concrete is very stable. Research results indicated that the porosity of hardened concrete meets the European standards for frost-resistant concrete. Research results of the influence of air- entraining admixture type have proved, that a greater amount of micro pores in concrete is the effect of a synthetic air-entraining admixture. In concrete with synthetic entraining admixtures the air pores have smaller diameters than in concrete with natural air-entraining admixture, which are being transferred into their specific surface. The synthetic admixture is more recommended than the natural one also because of the value of the air-voids spacing factor of concrete.

Effects of rotational shearing on rheological behavior of fresh mortar with short glass fiber

Shear stresses are always applied to fresh concrete during mixing and transporting processes, which have significant influences on the dispersion and agglomeration of cement particles. In this study, the effects of rotational shear mixing on rheological properties of fresh short glass fiber reinforced mortars with different mineral admixtures (containing fly ash and silica fume) were experimentally investigated. The shear rates of 50 s−1, 100 s−1 and 150 s−1 were selected as the rotational shearing rates. The Herschel-Bulkley model was used to characterize the rheological behavior of fresh glass fiber reinforced mortar. Results showed that the shear-thickening intensity increased with the increase of glass fiber volume fraction for the cement-fly ash binary mortar, while the addition of glass fiber resulted in the rheological behavior of cement-silica fume binary mortar changed from shear-thickening to shear-thinning response. After subjecting to rotational shear mixing, the measured shear stress was significantly increased and the fresh mortars with glass fibers easily showed shear-thickening behavior.

Influences of aggregate micro fines on the packing of fresh mortar and the performances of mortar

Water was regarded as the particle that its size is the minimum. According to the size of particle, the particles in the fresh mortar were divided into three grading: water, powder, and sand. The physical model of fresh mortar were established through the two-stage filling of particles, that is to say, the paste fills the voids of sand particles, water fills the voids of the powder particles in the remainder paste, and the remainder water is called as the surplus water. To calculate the remainder water in fresh mortar, the mathematical model of the packing was established to quantitatively characterize the physical filling effect of AMF in fresh mortar. On this basis, the manufactured fine aggregate (MFA) mortars with different water-to-cement (W/C) ratio (0.45, 0.50, 0.60, and 0.65) and different sand-to-cement (S/C) ratio (3:1, 2:1, and 1:1) were taken as the research object, and the influences of the AMF on the surplus water, bulk density, and mechanical property were studied when its content is respectively 0 wt%, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, and 30 wt% in MFA. The results show: the physical filling effect of AMF in fresh mortar can be better characterized with the volume of surplus water in fresh mortar, and the influence of the AMF on the packing of fresh mortar is better consistent with the bulk density of fresh mortar and the mechanical property of hardened mortar. This is the good references for the packing characterization of fresh mortar and the content determination of AMF in MFA.

Effects of Chemical Admixtures on the Working and Mechanical Properties of Ordinary Dry-Mixed Mortar

The effects of hydroxypropyl methyl cellulose ether, starch ether, bentonite, and redispersion emulsoid powder on the working and mechanical properties of fresh dry-mixed mortar were studied. The results show that hydroxypropyl methyl cellulose ether has the greatest impact on the consistency and water retention of ordinary dry-mixed mortar and that redispersion emulsoid powder reduces the water action and starch ether has essentially no effect on water retention. It also shows that the time of mortar condensation when mixed with hydroxypropyl methyl cellulose ether is the longest, followed by redispersion emulsoid powder and bentonite. Starch ether can slightly, but not obviously, extend the setting time of cement mortar. Hydroxypropyl methyl cellulose ether has the greatest impact on the mechanical properties of ordinary dry-mixed mortar, followed by redispersion emulsoid powder, starch ether, and bentonite. As the water retention increases, the setting time of the mortar also increases. The use of water as a thickening material has a retarding effect on the mortar, increases the water-retention rate, and increases the retarding effect. Moreover, increasing the content of the chemical admixtures decreases the strength of cement mortar.

Performance evaluation of sustainable high strength mortars incorporating high volume waste glass as binder

This study investigates the performance of sustainable high strength mortars incorporating recycled waste glass as a supplementary cementitious material (SCM) to replace cement from low (10%) to high (60%) replacement ratios, while mortars with conventional mix design are used as reference. The addition of the recycled waste glass significantly improves the slump-flow of fresh mortars in the presence of superplasticizer (SP). The increase of the recycled waste glass dosage contributes to the longer initial and final setting time compared to the plain cement sample. The high volume recycled waste glass containing sample shows an obvious delay of hydration compared with others incorporating the same amount of SP. The high strength series samples containing various contents of recycled waste glass show similar total gel porosity, but a significant increase of gel porosity was observed in the normal strength series samples containing recycled waste glass. From the SEM images, it can be identified that high dosage recycled waste glass-containing high strength mortars show a denser microstructure compared to the plain sample. The higher mesopore volume introduces higher drying shrinkage in sustainable mortars. The mechanical performance tests show that sustainable high strength mortars containing 60% recycled waste glass can achieve a satisfactory strength (99 MPa) compared to the plain cement sample (115 MPa).

Development of Strength for Calcium Aluminate Cement Mortars Blended with GGBS

In the present study, the development of strength in different calcium aluminate cement (CAC) mixture mortars with granulated ground blast-furnace slag (GGBS) was investigated. The substitution of GGBS levels was 0, 20, 40, and 60% weight of binder, of which the CAC used in this study naturally contained C2AS clinker as a secondary phase. To activate a hydraulic nature of the phase, in addition to the mineral additive, all specimens were cured at 35 ± 2°C for the first 24 hours and then stored in a 95% humidity chamber at 25 ± 2°C. The penetration resistance of fresh mortar was measured immediately after pouring, and the mortar compressive strength was monitored for 365 days. Simultaneously, to evaluate the hydration kinetics at early ages, in terms of heat evolution, the calorimetric analysis was performed at the isothermal condition (35°C) for 24 hours. The hydration behavior in the long term was characterized by X-ray diffraction, which was supported by microscopic observation using scanning electron microscopy with energy dispersive spectroscopy. Furthermore, an examination of the pore structure was accompanied to quantify the porosity. As a result, it was found that an increase in the GGBS content in the mixture resulted in an increased setting time, as well as total heat evolved for 24 hours in normalized calorimetry curves. In addition, the strength development of mortar showed a continuous increased value up to 365 days, accounting 43.8–57.5 MPa for the mixtures, due to a formation of stratlingite, which was identified at the pastes cured for 365 days using chemical and microscopic analysis. However, GGBS replacement did not affect on the pore size distribution in the cement matrix, except for total intrusion volume.

A model about dynamic parameters through magnetic fields during the alignment of steel fibres reinforcing cementitious composites

The aim of this paper is to perform a model to understand and to predict the dynamic behaviour of steel fibres immersed in fresh cementitious materials when exposed to Homogeneous Magnetic fields. Fibres behaviour is of especial interest to improve and develop a method to achieve the alignment of fibres in reinforced composites by means of magnetic fields. The torques and forces that a magnetic field summit a ferromagnetic fibre during its alignment find an opposition, in a fresh cementitious composite considered as a Bingham fluid: shear rate (γ̇) and yield stress (τo) and plastic viscosity (η). The torque necessary to rotate a single fibre is determined through a rotational rheometer and the relation between its geometry and the fresh cement rheology is determined. In this work, the alignment of fibres under magnetic fields within the range of 20 mT to 80 mT immersed in fresh mortars and fresh cements is studied. The orientation factor of the fibres after the magnetic field has been obtained. The probabilities of success depending on the initial angle of the fibres are also showed. The model to predict the alignment of fibres in cement-based materials presented here can be used also for different magnetic and rheological ranges.

Basic Research of Improving the Mortar Flow by Thermal Stimulation to Superplasticizer

Polycarboxylic acid-based superplasticizers are being used for various fields of concrete work, however little has reported on changing basic performance by thermal fluctuation. In this study, heating superplasticizers itself is hereinafter as referred to as “thermal stimulation”, the effect of thermal stimulation and heat retention of superplasticizer on the fresh mortar, moreover the influence of molecular structural changed of superplasticizer by thermal stimulation were investigated. As the result, it was confirmed that improving fluidity of the mortar flow on this condition the highly heat temperature and heat over a long time by thermal stimulation of superplasticizer. In addition, it turned out that this phenomenon was caused molecular structural changed by thermal stimulation, and the result was revealed that the effect of thermal stimulation varies according to the type of polymer.

Prediction of the swelling capacity of salt-insensitive superabsorbent polymers in concrete by rheological measurements

A study on the macroscopic viscosity of a flowable, fine-grained high-strength mortar was conducted in order to estimate the swelling capacity of two salt-insensitive superabsorbent polymers (SAPs). In doing so, rotational rheometer measurements of the mortar modified with dry pre-mixed SAP were performed at several water-to-cement ratios (W/C), i.e. in the range 0.32 to 0.40. The swelling capacity of each SAP was estimated by correlating the fitted macroscopic viscosity vs. solid particle fraction curve with the curve of the plain mortar without addition of SAP, produced at the same W/C. The swelling capacities were found to yield 28 g pore water per g dry SAP (g/g) and 35 g/g, respectively. In addition to this new approach, two more practical relevant test methods were evaluated with respect to swelling capacity: first, comparative mortar spread tests, which were based on the use of the same fresh mortars but with less amount of superplasticizer, and second, tea bag tests with plain SAP immersed in an artificial pore solution. Only minor differences were found for the estimated swelling capacities. Hence the conclusion may be drawn that all three test methods are suitable for determining the swelling capacity of SAP in a cementitious environment.

Influence of waste marble powder as a replacement of cement on the properties of mortar

The demand for cement usage increases in the world, currently. It is known that using industrial waste materials in concrete as cement or aggregate replacement as part of waste management as well as conserving natural resources is getting wider. Due to these facts, in this work, an investigation was carried out on the utilization of waste marble powders as cement replacement mineral materials. In this context, marble powder replaced cement at 5%, 10%, 15% and 20% in mass basis, and mortars were produced. In mortar mixtures, water-binder ratio was chosen as 0.5, and sand-binder ratio was taken as 3. Workability of fresh mortar was measured. Unit weight, water absorption, and porosity, compressive and flexural strengths, abrasion, carbonation and drying shrinkage measurements testing were carried out on hardened mortar specimens. Influence of elevated temperature on hardened mortar mixture was also investigated. As a result of laboratory study, it is concluded that replacing marble powder with cement result with a favourable contribution to workability of fresh mortar, as well as resistance to elevated temperature. It also reduced drying shrinkage of mortar in comparison to reference mortar made without marble powder. However, it influenced water absorption, abrasion, and carbonation resistance of mortar, unfavourably. For short term curing duration, replacement of marble powder with cement reduced compressive strength insignificantly for 5% and 10% marble powder replacement, but, reduced it significantly for 15% and 20%. However, at long term curing at 90 days, the difference between strength of reference mortar and marble containing mortar was diminished, particularly for mortar containing 5% and 10% marble powde

Utilization of gypsum from construction and demolition waste in Portland cement mortar

Abstract Civil construction generates the largest amount of construction and demolition waste (CDW), most of which is not reused and is discarded as inert waste in landfills. The purpose of this study was to evaluate the feasibility of reusing gypsum recovered from CDW in the preparation of mortar. This material was examined to determine its specific mass, morphology, elemental composition and particle size distribution. Test specimens were prepared with a mix design of 1:3 (cement:sand), with the gypsum waste substituting part of sand in proportions of 0, 10, 20 and 30% (in volume). The consistency of the fresh mortar was evaluated: the specimens were tested to determine their flexural and compressive strength, apparent density, water absorption, voids index, and specific mass. After 28 days, the mechanical strength of the specimens exceeded the limits specified by NBR 13281 standard, indicating that up to 30% of ground gypsum waste can be included in a mortar.

Lime render, shrinkage cracks and craftsmanship in building restoration

Abstract The present project concerns early shrinkage cracks in renders. This problem relates to the type of lime and rendering methods used in Sweden during the 19th and early 20th century as well as in current restoration practice. Results from different render restoration projects have indicated that a high frequency of shrinkage cracks could be related to the slaking procedure and the reworking of the slaked lime putty. The aim of the project was to investigate whether there is a connection between different handling procedures for wet-slaked lime putty and early shrinkage cracks in render. An investigation involving practical application and a laboratory test programme was initiated to examine the problem of early shrinkage cracks in renders based on wet-slaked sub-hydraulic lime. This type of lime was commonly used in Sweden in the 19th century. The laboratory work in the project included 3 different mix proportions based on reworked and non-reworked lime putty. The renders were applied after 1, 8, 15, 32 and 68 days storage of the lime putty. This gave 30 mortar mixes applied as rendered test surfaces. The flow number of the fresh mortars was determined and the workability, mixability and open time were assessed. The frequency of shrinkage cracks in the rendered surfaces was measured. The results showed that the frequency of shrinkage cracks was related to the methods applied in the slaking process and the storage time. Reworking and storage of the lime putty increased the frequency of shrinkage cracks. The properties of the fresh mortar were also influenced.

A method to determine water absorption of recycled fine aggregate in paste for design and quality control of fresh mortar

The high absorption of recycled fine aggregate (RFA) directly affects the effective W/C ((W/C)eff) of paste in cement-based materials, giving poor fresh state consistency and affecting the mechanical behavior in the hardened state. A novel method was proposed to determine the water absorption of RFA in fresh paste (WAp) at plastic stage in this paper, which was calculated by the difference of total water content of paste between the mixture incorporating the RFA and the reference cement paste. Three series of mortars were prepared respectively for investigating the influence factors on the WAp, considering the absorption capacity of RFA in water at 24 h (WA24h), W/C (0.35, 0.45, 0.55) of fresh paste and A/C (1, 2, 3) of the proportions. The results show that the water absorption of RFA in paste and its evolution is lower than that in water, being up to 44.38%–80.18% of WA24h at 1 h. In the first 5 min, the WAp reaches quickly to the 36.34%–57.61% of WA24h. And it decreases when using RFA with smaller WA24h, and in the mixture proportions with a lower W/C and higher A/C. Based on the relationship between the WAp and these factors, the (W/C)eff of mortar with dry RFA can be estimated in different mixtures. Conversely, the additional water for a better workability can be also calculated with the proposed W/C, which has been verified by the testing results for total water content of paste in various mortars. The corresponding reduction of water absorption in paste should be taken into account during the mixture design with RFA.

Digital image correlation (DIC) on fresh cement mortar to quantify settlement and shrinkage

The displacement of fresh cementitious media initiated by water evaporation and cement hydration is very complex. In the plastic state, the cement particles deform in the plane and move at different rates leading to the development of plastic shrinkage cracks. In parallel, the material settles as bleed water is released. Tracking the particles three-dimensional heterogeneous displacement requires a highly-sensitive monitoring technique. Digital image correlation (DIC) has been selected to quantify settlement and shrinkage strain evolution. DIC excels compared to classical LVDT point-transducers since it is non-contact and the analysis is full field providing a three-dimensional (3D) view of deformations and strains. 3D visualization maps of early-age deformation contribute to the interpretation of early age mobility. DIC enables the measurement of non-uniform surface displacement due to material heterogeneity and geometry that affects the shrinkage distribution which cannot be detected by traditional LVDTs. The procedure through which the DIC speckle pattern is applied on a wet rough surface is critically discussed.

Space Truss Masonry Walls With Robotic Mortar Extrusion

This work presents a generalized method for robotic mortar extrusion, allowing the fabrication of structural-insulating walls of novel performances. It involves two distinct steps that are to be simultaneously automated: extrusion of a specifically formulated mortar, and assembly of adequately shaped insulating blocks. Here, the layer by layer approach of concrete printing is renewed by using insulating blocks as support for the extrusion. The volumetric space of the wall is divided by an adequate space tessellation, dividing it in polyhedra. They become insulating blocks, on the edges of which mortar is extruded. The set of edges then forms a space truss, of great mechanical efficiency. “Printable” mortar is crucial to the system for the blocks could not withstand the hydrostatic pressure of fresh mortar without additional form-work features, once a few meters height has been reached. This approach renews traditional confined masonry, allowing for geometric complexity and automation.

Effect of water absorption of SAP on the rheological properties of cement-based materials with ultra-low w/b ratio

Superabsorbent polymer (SAP) is an important internal curing agent for concrete with low or ultra-low water-to-binder ratio (w/b). When SAP is added, it will absorb water from fresh concrete fast. Thus, water absorption of SAP will affect the rheological properties of cement-based materials, especially at low w/b. Moreover, SAP with different particle size has a different absorption rate which will also affect the rheological properties. In this paper, two SAPs with different particle size are used to investigate its effects on the maximum shear stress, yield stress, plastic viscosity and thixotropy of cement-based materials within 80 min. Basic w/b of 0.18 was specified as reference values. Rheological results show that the absorption of SAP changed the evolution of yield stress, plastic viscosity and thixotropy of fresh mortar with time. Large SAP’s particles led to a high absorption rate and a long absorption time which increased the yield stress and plastic viscosity. The above effects of SAP are closely related to the availability of water near SAP in cement mortar which causes to be a nonlinear relationship between the amounts of SAP and extra water required. In addition, the amount of extra water should be adjusted according to particle size of SAP and the addition level of SAP.

Influence of non-adsorbing polymers on drying of fresh mortars

In this paper, we compare the drying of non-reactive materials (glass beads packing) with the one of fresh mortars. Through the sample drying process, the existing literature on the general underlying physical processes involved in drying of porous media allows for the identification of two distinct regimes. These regimes drive the drying kinetics. We then measure the drying kinetics of the same materials containing polymers, which do not absorb on the cement grains. Our results and analysis suggest that the increase in the viscosity of the interstitial water due to polymer addition is at the origin of a decrease in drying rate. As drying of fresh cementitious materials strongly impacts the final properties in configuration with large exposed surfaces, we suggest that such polymer addition could slow down the overall drying of cementitious materials and improve their service life properties.