Characterization Of Mortars Research Articles

Mechanical Characterization of Sustainable Mortars with Recycled Aggregates from Construction and Demolition Wastes: An Experimental Investigation

The use of recycled aggregates in the production of concrete and mortar represents a sustainable way to reintroduce these constituents—which are typically treated as waste and disposed of—in the production chain, providing new value to potentially polluting materials. The effect of recycled aggregates has been widely studied in the production of concrete due to the directions of National Standards in Italy; however, their role in the manufacturing of mortar must be investigated further due to the high variability that can be observed in the literature. In particular, the aim of this paper is the mechanical characterization of sustainable mortars defined by different mix designs and different binders, in which the aggregates are gradually replaced by a recycled sand obtained from the grinding of construction and demolition wastes, which could include old concrete, clay bricks, and minimal amounts of other kinds of residual materials. This investigation is carried out through experimentation, taking into account four different mortar compositions defined by an increasing percentage of recycled constituents. Virgin aggregates are also studied for the sake of comparison. The results, accomplished through a three-point bending test and an unconfined compression test, show that it is still possible to maintain acceptable mechanical properties by using these wastes as aggregates in spite of a decrease in the analyzed values. In general, the mean reductions with respect to the use of natural aggregates are about 30–40% and 35–55%, respectively, for compressive and flexural strengths. It should be highlighted that some experimental sets provide a maximum reduction of 70–80%, but the results are still within the limitations of the standards. This aspect can be considered to be a good compromise since the production of this sustainable construction material can represent a solution that is able to reduce the extreme exploitation of natural resources, the pressure on landfills, and the consumption of energy, which are related to the construction industry.

The Effect of Adding Banana Fibers on the Physical and Mechanical Properties of Mortar for Paving Block Applications

Paving blocks might encounter diverse environmental conditions during their lifespan. The durability of paving blocks is determined by their capacity to endure various exposure conditions. Synthetic fibers have been used in mortar and concrete to improve their properties. This research investigates the influence of including banana fiber (BF) on the physical and mechanical characteristics of mortar. Five different mortar mixes were developed, with varying amounts of BF ranging from 0 to 2% by volume. Testing included ultrasonic pulse velocity, compressive strength, flexural strength, total water absorption, and sorptivity. Specimens were cured for up to 90 days. The results indicate that using 0.5% BF resulted in an improvement in compressive and flexural strength compared to the control mix. There was an increase in total water absorption and the water absorption coefficient in the presence of fibers. There appeared to be good correlations between the compressive strength and the other properties examined.

Development and Characterization of Lime-Based Mortars Modified with Graphene Nanoplatelets

Materials for the conservation of cultural heritage must meet specific demands, such as high durability, service life, and compatibility with other materials used in the original building structures. Due to their low permeability to water and water vapor and their high rigidity, the use of Portland cement (PC) mortars, despite their high mechanical resistance and durability, does not represent an appropriate solution for the repair of historic masonry and structures. Their incompatibility with the original materials used in the past, often on a lime basis, is therefore a serious deficiency for their application. On the other hand, lime-based mortars, compared to PC-based materials, are more susceptible to mechanical stress, but they possess high porosity, a high water vapor transmission rate, and moderate liquid water transport. This study aims at the development of two types of lime-based mortars, calcium lime (CL) and hydraulic lime (HL). The modification of mortars was conducted with a carbon-based nanoadditive and graphene nanoplatelets (GNs) in three dosages: 0.1%, 0.3%, and 0.5% of the binder weight. The enhancement of CL mortars by GNs greatly increased mechanical strength and affected heat transport characteristics, while other characteristics such as porosity, water absorption, and drying rate remained almost similar. The application of GNs to HL not only enhanced the strength of mortars but also decreased their porosity, influenced pore size distribution, and other dependent characteristics. It can be concluded that the use of graphene nanoplatelets as an additive of lime-based composites can be considered a promising method to reinforce and functionalize these composite materials. The improved mechanical resistance while maintaining other properties may be favorable in view of the increasing requirements of building materials and may prolong the life span of building constructions.

Analytical characterization of historical mortars from the Roman villa of Frielas (Loures, Portugal)

The analytical characterization of mortar samples from the Roman archaeological site of Frielas, located in Lisbon, Portugal; was carried out by means of X-diffraction (XRD), thermogravimetry (TGA-DTG), optical microscopy and scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM-EDS), acid attack and granulometric analysis. A total of eighteen mortar samples were collected from the different structures of the villa with different functional uses (render, filler, and floor). The results showed a similar composition of binder, while differences in aggregates allowed to establish several groups. Results were discussed as evidence of manufacturing techniques, production technologies, and provenance of possible raw materials. There was no prominent variation that can suggest a different chronology between the group of samples. Though, it is assumed that there might be some renovation, restoration, or partial rebuilding that occurred in the same period. In terms of production technology, proportions ruled by Vitruvius were not followed.

Mechanical and shrinkage properties of alkali-activated mortars with graphite tailings

To improve the problems of high CO2 emission generated by the preparation of silicate cement, large accumulation of solid waste, and depletion of natural sand resources, this paper investigates the effect of pozzolanic effect of graphite tailings (GT) on the mechanical properties, shrinkage properties and microstructure of alkali-activated mortar, and less research has been done on this related content. This paper partially replaced the natural sand with GT, and completely replaced the cement with fly ash and slag to prepare alkali-activated fly ash-slag (AAFS) mortar. The consequences of GT replacement rate on the mechanical and shrinkage characteristics of AAFS mortar were analyzed. In addition, X-ray diffraction (XRD), mercury-in-pressure (MIP), and nuclear magnetic resonance (29Si MAS NMR) were used to examine the hydration degree, pore structure, and hydration products of AAFS mortar. The results demonstrated when the Na2O content was 7 % and the activator modulus was 1.0, the test group's 28-day flexural and compressive strengths at a 20 % GT replacement rate were increased by 19.49 % and 14.45 %, respectively, compared to the test group without GT. The appropriate quantity of GT reduced the AAFS mortar's drying shrinkage and increased the AAFS mortar's self-shrinkage. According to the microstructure analysis, GT had a pozzolanic effect: moderate doping of GT promoted the hydration reaction of precursors, improved the amount of C-(A)-S-H gel product generated, and improved AAFS mortar's mechanical and shrinkage properties.

Random distribution of asphalt and cement mortar in semi-flexible pavement: Implication for cracking resistance

The distribution characteristics of asphalt and cement mortar play a crucial role in determining the cracking resistance of semi-flexible pavements (SFP). In this study, digital image processing technology was utilized to quantify the thickness distribution of asphalt and cement mortar within SFP, and a parallel line segmentation method was employed to characterize the random distribution of mortar thickness (RDMT) of asphalt and cement mortar. Variance, coefficient of variation (COV), and interquartile range were proposed to characterize RDMT, examining the effects of air voids (AV) content, nominal maximum aggregate size (NMAS), and compaction method on RDMT, and its variation along the specimen height. Semi-circular bending test was conducted to evaluated the cracking resistance of SFP, exploring the relationship between RDMT and cracking resistance. Results indicate that parallel line segmentation method with 36 parts and 25 parts is recommended to characterize the RDMT of asphalt and cement mortar, respectively. An increase in AV content led to a higher RDMT for asphalt mortar but a lower RDMT for cement mortar. Conversely, as NMAS increased, the average thickness of asphalt and cement mortar increased, while the RDMT of asphalt mortar decreased and that of cement mortar increased. RDMT of asphalt and cement mortar is higher under Superpave gyration compaction method compared to the Marshall compaction method. Additionally, RDMT increased from the top to the bottom of the specimen height. Based on the RDMT, a random distribution index (RDI) was proposed, which exhibited a strong linear relationship with the cracking resistance of SFP. When the RDI decreased by 44.4 %, the corresponding cracking resistance of SFP increased by 84.0 %. Improving the distribution of asphalt and cement mortar could enhance the cracking resistance of SFP.

A new multi-analytical procedure for radiocarbon dating of historical mortars

The overarching challenge of this research is setting up a procedure to select the most appropriate fraction from complex, heterogeneous materials such as historic mortars in case of radiocarbon dating. At present, in the international community, there is not a unique and fully accepted way of mortar sample preparation to systematically obtain accurate results. With this contribution, we propose a strategy for selecting suitable mortar samples for radiocarbon dating of anthropogenic calcite in binder or lump. A four-step procedure is proposed: (I) good sampling strategies along with architectural and historical surveys; (II) mineralogical, petrographic, and chemical characterization of mortars to evaluate the feasibility of sample dating; (III) a non-destructive multi-analytical characterization of binder-rich portions to avoid geogenic calcite contamination; (IV) carbonate micro-sample preparation and accelerator mass spectrometer (AMS) measurements. The most innovative feature of the overall procedure relies on the fact that, in case of positive validation in step III, exactly the same material is treated and measured in step IV. The paper aims to apply this procedure to the ancient mortar of the Florentine historical building (Trebbio Castle), selecting micro-samples suitable for dating in natural hydraulic mortars. The discussion of the mortar dating results with the historical-archaeological hypotheses provided significant insights into the construction history of the building.

Transition coefficients during bending testing of samples for mortars and fine-grained cement concretes

Introduction. Existing cement mortars and fine-grained cement concretes have the same composition, however, according to State Standard, these materials are tested using different methods for evaluating physical and mechanical properties that are not in harmonious accordance with each other. This disagreement in the evaluation of properties confuses the regulatory authorities, which receive data that contradict each other. The introduction describes the appearance of discrepancies in the assessment of the properties of fine-grained cement concrete and cement mortar. A change in the concepts of definitions between the original classification and the modern one is presented. Aim. Finding the transition coefficients when testing for three-point and four-point bending of samples of mortars and fine-grained cement concrete, taking into account the geometric dimensions of the samples. Materials and methods. Preparation of cement concrete samples of various classes of materials conforming to State Standard requirements, description of differences in methods for determining three-point and four-point bending, calculation and manufacture of additional installations taking into account the geometric dimensions of the samples, conducting bending tests according to standard methods and using manufactured installations preserving the proportion of values taking into account the scale of the sample, as well as calculation of transition coefficients for each class. Results. The results of the study showed that the transition coefficients have a significant impact on the processing of the results and the assessment of the strength characteristics of mortars and fine-grained cement concretes and may affect the accuracy of the data obtained. Conclusions. The study provides a better understanding of the mechanical properties of mortars and cement concretes during bending, which can be useful in the design, construction of structures and quality control.

Construction biotechnology: improving mortar properties through calcium carbonate precipitation using a novel strain of the bacterium Neisseria perflava

In construction technology, there are significant efforts to reduce environmental emissions, particularly NH3 and other pollutants. This study marks the first application of CaCO3 biomineralization biotechnology in microbially induced calcium carbonate precipitation (MICCP) to enhance mortar properties using the non-pathogenic Neisseria perflava strain SKC/VA-3, which employs carbonic anhydrase mechanisms. The results demonstrated that N. perflava could significantly improve the physical and mechanical characteristics of mortar. Incorporating N. perflava and calcium lactate pentahydrate resulted in a 20% increase in compressive strength and a 14% rise in indirect tensile strength of the mortar. Examination through scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM–EDS) revealed calcite formation within the microstructure of the bio-mortar. Additionally, self-healing assessments indicated that calcite precipitation, driven by bacterial metabolism, also occurred on the cracked surfaces of the bacterial mortar, suggesting potential for reduced maintenance and increased material longevity. This study provides the first report on the use of N. perflava for bio-mortar enhancement and represents a novel biotechnological approach to improving the properties of mortar and other cementitious materials. The utilization of N. perflava in bio-mortar represents a groundbreaking biotechnological advance, potentially enhancing mortar and other cement-based materials. This development contributes to sustainable, durable, and environmentally friendly construction technologies.

Inhibiting efflorescence of alkali-activated slag mortar by improving its hydrophobicity with methyl-terminated polydimethylsiloxane (PDMS): Evidences showing the remained PDMS

This paper proposes to prepare hydrophobic alkali-activated slag (AAS) mortars with methyl-terminated polydimethylsiloxane (PDMS), a hydrophobic polymer with low surface energy, to minimize its water sorptivity and efflorescence. To depict the efflorescence process of PDMS-modified AAS mortars, visual inspections of efflorescence features, the leaching behavior of sodium ions, water absorption characteristics of mortars and contact angle tests were conducted. Additionally, the hydration process, microscopic morphology, and chemical structure of PDMS-modified AAS mortars and pastes were examined by compressive strength, isothermal calorimetry, TEM, SEM, FT-IR, 29Si NMR, enabling the explanation of PDMS working mechanisms. The results demonstrated that the addition of PDMS successfully mitigated esthetic issues and the spalling of mortars caused by efflorescence. Furthermore, PDMS reduced the risk of long-term durability issues of AAS mortars by restricting the loss of sodium ions after efflorescence. At the same time, the introduction of PDMS with dosage below 5 % did not significant retarder the hydration reaction process or the development of strength of AAS. However, it did alter the micromorphology and chemical structure of the hydration product. PDMS linked to the hydration products through covalent bonds and acted as a bridging role to alter the micromorphology of the hydration products. The resulting multi-structured material exhibited micropapillary and nano-coating layers with hydrophobic methyl functional groups, imparting hydrophobicity to the PDMS-AAS hydration product.

Characterization of historic mortars and the effect of rice husk ash (RHA) on quicklime

Historic mortars are minerologically characterized for many reasons pertaining to traditional building conservation. In order to determine the binding material of the historic masonary building, this material must be sufficiently separated from the aggregate. In this study, the Cas mortar (Traditional gypsum-based construction mortar in Siirt, Türkiye) used in traditional Cas houses was characterised and compared with composite lime mortars prepared by substituting quicklime with 10 %, 15 % and 20 % rice husk ash (RHA). The mechanical properties of Cas mortar are much higher than those of lime mortars. However, when 20 % RHA was substituted for lime, it was found to significantly change the properties of the mortars, increasing the compressive and flexural strength by 68 % and 58 % respectively and improving the specific heat and many other properties. X-ray diffraction (XRD), thermogravimetric analysis (TGA) and differential thermal analysis (DTA) and Fourier transform infrared spectroscopy (FT-IR) analyses showed that the 63 μm sieved powder analysis was more accurate in determining the chemical characterisation of the historic mortars.

Simultaneous Effect of Diameter and Concentration of Multi-Walled Carbon Nanotubes on Mechanical and Electrical Properties of Cement Mortars: With and without Biosilica.

In this work, the effect of multi-walled carbon nanotubes (MWCNT1, MWCNT2, and MWCNT3) with different outer diameters and specific surface areas on the mechanical and electrical properties of cement mortar have been investigated. Various concentrations of MWCNTs were used (0.05, 0.10, and 0.15%), the effective dispersion of which was carried out by an Ultrasonic machine (for 40 min with 160 W power and a 24 kHz frequency) using a surfactant. Composites have been processed with a biosilica content of 10% by weight of cement and without it. Compressive strength tests were carried out on days 7 and 28 of curing. The 7-day compressive strength of samples prepared without biosilica increased compared to the result of the control sample (6.4% for MWCNT1, 7.4% for MWCNT2, and 10.8% for MWCNT3), as did those using biosilica (6.7% in the case of MWCNT1, 29.2% for MWCNT2, and 2.1% for MWCNT3). Compressive strength tests of 28-day specimens yielded the following results: 21.7% for MWCNT1, 3.8% for MWCNT2, and 4.2% for MWCNT3 in the absence of biosilica and 8.5%, 12.6%, and 6.3% with biosilica, respectively. The maximum increase in compressive strength was observed in the composites treated with a 0.1% MWCNT concentration, while in the case of 0.05 and 0.15% concentrations, the compressive strengths were relatively low. The MWCNT-reinforced cement matrix obtained electrical properties due to the high electrical conductivity of these particles. The effect of MWCNT concentrations of 0.05, 0.10, and 0.15 wt% on the electrical properties of cement mortar, especially the bulk electrical resistivity and piezoresistive characteristics of cement mortar, was studied in this work. At a concentration of 0.05%, the lowest value of resistivity was obtained, and then it started to increase. The obtained results show that all investigated specimens have piezoresistive properties and that the measurements led to a deviation in fractional change in resistivity.

Enhancement of mortar’s properties by combining recycled sand and limestone calcined clay cement

The use of Recycled Fine Aggregate (RFA) combined with Limestone-Calcined Clay Cement (LC3) is one of the low-carbon options for replacing ordinary mortar, leading to an eco-friendly and sustainable construction material, and providing a solution for waste management. In this paper, a comprehensive investigation concerning the mechanical properties and microstructural characteristics of LC3 mortar, using different proportions of limestone, calcined clay, cement clinker, and two types of RFA (namely RS1 and RS2), was carried out. The results highlight that a binder with 17.55 wt% calcined clay, 8.77 wt% limestone, and 73.68 wt% CEM I shows superior mechanical properties compared to CEM I with both natural sand and high-quality recycled sand, and similarly it shows better mechanical properties than CEM II at all levels of substitution of natural sand with recycle sands of high and normal quality. The replacement of commercial cement with LC3 mitigates the negative impact of RFA on water absorption, enhances pore size distribution, reduces total porosity, and boosts mechanical strength. The combination of RFA with LC3 is an effective approach to reduce the environmental impacts of cement production, to well manage wastes generated by construction and demolition, and to improve material’s performances.

Research on influence laws of aggregate sizes on pore structures and mechanical characteristics of cement mortar

Aggregate plays an important role in cement-based materials. Evaluating the impact of aggregate gradation on pore structure and mechanical properties will help to optimize the mortar ratio and improve its durability. In this study, artificial sand with 5 different particle sizes was used as aggregate, and the synthetic gradation formed by their coupling was compared. The pore structure distribution of mortar was quantitatively characterized by nuclear magnetic resonance (NMR) technology. Surface-to-volume ratio (SVR) and ρd (aggregate packing density) were used to characterize the aggregate grading characteristics. The correlation between aggregate gradation characteristics and mortar parameters, such as porosity, pore structure fractal dimension, permeability coefficient, and mechanical strength, was analyzed, and a compressive modulus of mortar was established. The results indicate that the pore structure characteristics, K (permeability), and mechanical characteristics of mortar are all influenced by both SVR and ρd. The predominant pores in the mortar are micropores and movable fluid pores, and the addition of 0.1–0.5 mm aggregates reduces the formation of micropores, mesopores, macropores, and movable fluid pores in the mortar. As the number of pores increases, the complexity of the pore structure decreases, leading to higher homogeneity. Moreover, the K shows a strong power function relationship with the total porosity and the total porosity fractal. The compressive strength and Ec (compression modulus) of GM1–6 are significantly higher than those of GM7–9, correlating with the minimum aggregate size and the inherent strength of the aggregates. The regression results of the strength correlation model are significant, and the strength model established based on the porosity of micropores and Ec can accurately predict the compressive strength of mortar.

Analysis of Freeze-Thaw Damage of Cement Mortars Doped with Polyethylene Glycol-Based Form Stable Phase Change Materials.

The development of construction materials with the integration of phase change materials (PCMs) has been a topic of wide interest in the scientific community, especially in recent years, due to its positive impact on temperature regulation inside buildings. However, little is known about the behavior of materials doped with PCMs when exposed to accidental or severe environments. Currently, a large area of the planet experiences seasonal freeze-thaw effects, which impact the durability and performance of construction materials. Accordingly, the main objective of this study was to evaluate the damage caused by cyclic freeze-thaw actions on the behavior of a cement mortar, including a PEG-based form-stable PCM. An experimental methodology was developed based on the physical and mechanical characterization of mortars under normal operating conditions and after being subjected to freeze-thaw cycles. The results indicated that, under normal exposure conditions, the incorporation of aggregate functionalized with PCM led to a decrease in the mortar's water absorption capacity, compressive strength, and adhesion. However, its applicability has not been compromised. Exposure to freeze-thaw cycles caused a loss of mass in the specimens and a decrease in the compressive strength and adhesion capability of the mortar.

Mechanics and microstructure analysis of geopolymer utilizing ilmenite tailing and metakaolin powder as alkali-activated materials

Geopolymers derived from bulk solid waste are considered ideal substitutes for cement-based materials in developing environmentally friendly construction materials. The utilization of solid waste tailings powder as a precursor for alkali activation of geopolymer can enhance the mechanical characteristics of geopolymer. This study conducted extensive experimental studies on the compressive strength, flexural strength, SEM microstructure, thermogravimetric curve, and variable influence of alkali-activated ilmenite tailings (IT) geopolymer mortar, using the liquid-solid ratio and the number of tailings as variables. An analysis was conducted on the mortar's mechanical characteristics, microstructure, and machine-learning properties. Furthermore, the impact of different atomic ratios on the structure and characteristics of geopolymer mortars was also examined. The test results revealed that the metakaolin-iron titanium tailings geopolymer, when doped with 10% ilmenite tailings, exhibited a compressive strength of 72.30MPa at 14 days. Similarly, the flexural strength of the geopolymer reached 4.76MPa at 14 days when doped with 30% ilmenite tailings. XRD analysis showed that Magnesiohornblende particles Mg-F-A-S-H and C-A-S-H gel had positive and negative correlations, respectively, with the tailings doping level. TG results indicated that the specimens exhibit enhanced thermal stability following treatment with tailings. SEM analysis revealed that combining ilmenite tailings with metakaolin formed Me-(F)-A-S-H gels. The examination of surface porosity, pore shape, and unreacted material determined that adding ilmenite tailings increased the Si/Al and Fe/Si ratios, enhancing the transformation of the lamellar structure to the three-dimensional disordered gel mesh structure. Additionally, the tailings contributed a significant amount of Ca, elevating the Ca/Na ratio (0.1−0.6) and triggering calcium precipitation within a Ca/Si range of 0.03−0.2. This increase in calcium led to a decrease in the sample's strength as the curing time was extended. Based on prior research and the application of the Gray Wolf optimization algorithm in extreme learning, a clear negative correlation was identified between the liquid-solid ratio and strength. Furthermore, increasing the Si/Al ratio enhanced the geopolymer's strength, while an extended curing time negatively correlated with strength. The impact of tailings mixing was deemed insignificant when the tailings amount did not exceed 20%. Geopolymers may derive significant environmental and industrial benefits from the improvement of their mechanical properties, thermal stability, and optimization using machine learning.

Physico-Mechanical Characterization of Masonry Mortars for Sustainable Construction: Experimental Study with Four Different Aggregates

The construction sector generates a strong environmental impact every year as a result of the high consumption of raw materials and the large waste volumes associated with this productive activity. In this sense, the search for alternative and sustainable solutions that allow progress towards responsible economic growth has become a priority activity. This work presents an exhaustive characterisation of masonry mortars made with four different types of aggregates: standard sand, natural sand, concrete waste recycled sand and ceramic components recovered sand. Differently from other studies, this research addresses the previous characterisation of the aggregates as raw material for the manufacture of masonry mortars, and, afterwards, a study of the most relevant properties for these cement composites in the fresh and hardened state is carried out. The most relevant properties of the mortars made with these raw materials are presented, and the repercussion of aggregate washing on their physical-mechanical characteristics is analysed. The results show how mortars made with 100% recycled aggregate can be competitive in the industry, presenting excellent properties in the fresh state and achieving an optimal mechanical strength. In addition, it has been observed that the introduction of a previous washing step of the aggregates improves their physical-mechanical properties and results in a higher quality of the cement mortars finally produced. In this way, the most representative properties of this type of materials have been collected in a well-structured and complete way, thus showing their possibilities of application in the construction industry.

Optimizing Masonry Mortar: Experimental Insights into Physico-Mechanical Properties Using Recycled Aggregates and Natural Fibers

The European Green Deal establishes the efficient management of construction resources as one of its main lines of action. In this sense, the recovery of construction and demolition waste for its reincorporation into the manufacturing process of new sustainable materials has become necessary for the industry. This work deals with the physical and mechanical characterization of cement mortars made with recycled concrete aggregates and reinforced with natural fibers. The reinforcement fibers used (abaca, coconut, and toquilla) are more environmentally friendly compared to traditional synthetic reinforcements. The aim of this research is to analyze the main physico-mechanical properties of these sustainable cement mortars. The results show that mortars made with recycled sand have a lower density and better thermal performance than traditional mortars. In addition, with the incorporation of these natural fibers, the flexural strength of the mortars with recycled aggregate increased by up to 37.6%. Another advantage obtained from the incorporation of these natural fibers is the reduction in shrinkage in the masonry mortars during the drying process, giving them greater dimensional stability and making their behavior similar to that of traditional mortars. Thus, this work shows the potential application of masonry mortars produced under circular economy criteria and their application in the building sector.

Ultrasonic velocity and density measurement for mortar characterization: Investigation of correlations with mortar porosity and sand grain size

Ultrasonic velocity and density measurement for mortar characterization: Investigation of correlations with mortar porosity and sand grain size

Improved mechanical properties and fiber dispersion of limestone calcined clay cement (LC³) mortars by adjusting the mixing methods

An emerging cement, limestone calcined clay cement (LC³), reduces CO2 emissions by using less clinker in manufacture, promoting sustainability. Compared with OPC, LC³ binders (with the same water-to-binder ratio) show reduced flowability, leading to poor fibre dispersion in the matrix. This paper attempts to improve the flowability by adding different amounts of superplasticizer and using an innovative two-phase water addition (TPWA) mixing approach. This method focuses on adjusting the amount of water addition in the first phase to improve the fibre distribution while maintaining the total water addition for all mixtures. Results show that modified mixing strategies improve the fresh and hardened characteristics of LC³ mortars. As the amount of water addition (in the first phase) decreases, the yield strength increases while the plastic viscosity of mortars decreases. The high yield stress is associated with high fibre segregation resistance during the compaction. The low plastic viscosity is related to high fibre mobilizability during mixing, preventing fibres from clustering. As a result, the humongous mixture and the best mechanical performance was achieved when 83 % of the total water was added in the first phase, with a w/b ratio of 0.35. For the mixture with a w/b ratio of 0.38, the best mechanical properties were obtained when 68 % of the total water was added in the first stage. The relationships between rheological properties, fibre dispersion and mechanical properties of LC³ systems are also established.