Concrete Equivalent Mortar Research Articles

Resting time effects on flow properties of cementitious materials: a study on self-compacting concrete equivalent mortar made with recycled aggregates

The concrete equivalent mortar (CEM) method, mainly used in the laboratory, offers a course that facilitates and accelerates experimental test programs with relatively small amounts of materials. To this end, two CEM mixes, with natural and recycled aggregates, at different superplasticizer (SP) concentrations, were tested. The key objective was to investigate how CEM flow property changed at 0, 30, and 60 min of resting time, emphasizing the material’s structuring and destructuring effects. This study describes the flow behaviour of CEMs applying specific tools. Also, a vane-geometry rheometer was used to obtain rheological flow curves. Whatever the SP content in the structuring state, the results indicated reduced flow properties over time. However, an SP content of 1.3% retard the structural build-up property that was not evident at 60 min-rest time. Spread diameters ranging between 300 and 400 mm are measured with the mini cone immediately after mixing. After 60 min of resting time, these diameters were reduced between 260 and 300 mm. Remixing after prolonged rest periods reduces the flow stress values, which decrease from 10 to 18 Pa to 6 to 14 Pa. After a structural build-up at a rest time, the structural break-down effect by remixing re-fluidifies the mixtures. The fluidity has recovered its initial state, reflecting a thixotropic property.

Effectiveness of the Concrete Equivalent Mortar Method for the Prediction of Fresh and Hardened Properties of Concrete

Modern concrete mix design is a complex process involving superplasticisers, fine powders, and fibres, requiring time and energy due to the high number of trial tests needed to achieve rheological properties in the fresh state. Concrete batching involves the extensive use of materials, time, and the testing of chemical admixtures, with various methodologies proposed. Therefore, in some instances, the required design properties (physical and mechanical) are not achieved, leading to the loss of resources. The concrete equivalent mortar (CEM) method was introduced to anticipate concrete behaviour at fresh and hardened states. Moreover, the CEM method saves time and costs by replacing coarse aggregates with an equivalent sand mass, resulting in an equivalent specific surface area at the mortar scale. This study aims to evaluate the performance of fibre in CEM and concrete and determine the relationships between the CEM and the concrete in fresh and hardened states. Steel and polypropylene fibres were used to design three series of mixtures (CEM and concrete): normal-strength concrete (NSC), high-strength concrete (HSC), high-strength concrete with fly ash (HSCFA), and equivalent normal-strength mortar (NSM), high-strength mortar (HSM), and high-strength mortar with fly ash (HSMFA). This study used three-point bending tests and digital image correlation to evaluate load and crack mouth opening displacement (CMOD) curves. An analytical mode I crack propagation model was developed using a tri-linear stress–crack opening relationship. Post-cracking parameters were optimised using inverse analysis and compared to actual MC2010 characteristic values. The concrete slump is approximately half of the CEM flow; its compressive strength ranges between 78% and 82% of CEM strength, while its flexural strength is 60% of CEM strength. The post-cracking behaviour showed a significant difference attributed to the presence of aggregates in concrete. The fracture energy of concrete is 28.6% of the CEM fracture energy, while the critical crack opening of the concrete is 60% of that of the CEM.

Hybrid Nucleation Acceleration Method with Calcium Carbonate and Calcium Silicate Hydrate for Fast-Track Construction

This research focuses on achieving early strength of cement-based materials through the hybrid nucleation acceleration method. Through the study of various mortar mixtures, which incorporate components such as ordinary Portland cement (OPC), fine limestone powder (with a particle size of d50: 1 μm), coarse limestone powder (with a particle size of d50: 12 μm), calcium silicate hydrate (C-S-H) nucleation seeding agent, and calcium nitrate (CN), the effect of the hybrid nucleation acceleration method was investigated. When OPC was substituted with 20% fine limestone powder, a strength of 13.5 MPa was achieved at 6 h, whereas the use of coarse limestone powder only yielded 3.5 MPa within the same time frame. The mortar containing 2% C-S-H nucleation seeding agent reached an impressive 16 MPa at 6 h. Meanwhile, through the synergistic combination of fine limestone powder and C-S-H nucleation seeding agent, the 6 h early strength attained an impressive 19 MPa. The micrograph revealed that the hybrid nucleation acceleration method significantly promoted the formation of a dense network of C-S-H within the paste, thus enhancing the packing density. Measuring the heat release demonstrated that the samples accelerated with the C-S-H nucleation seeding agent and fine limestone reached the peak 160 min earlier than the OPC sample, indicating a faster hydration process. The hybrid nucleation accelerated concrete (HNAC) achieved strengths of 20 MPa and 27 MPa within 6 and 8 h, respectively, whereas the 28-day strength surpassed 70 MPa. The concrete equivalent mortar (CEM), derived from concrete, attained a compressive strength of 25 MPa within 8 h, making it suitable for repair applications. The modulus of rupture (MOR) was 7.31 MPa at 8 h and increased to 17.27 MPa at 28 days. Overall, the developed concrete and CEM with the novel hybrid nucleation acceleration method allowed for high early and long-term strength for fast-track construction to be attained.

New insight on rheology of self-consolidating earth concrete (SCEC)

Self-consolidating earth concrete (SCEC) is a novel alternative to facilitate the earth-based construction. A new concrete-equivalent mortar (CEM) approach with constant excess-paste (EP) thickness was proposed to evaluate the rheological and thixotropic properties of various SCEC mixtures proportioned with different clay and superplasticizer types. The use of non-esterified polycarboxylate (NE-PC) and sodium polynaphtalene superplasticizer types in combination with a finer clay type led to a thixotropic behavior. Mixtures made with sodium hexametaphosphate resulted in significantly high yield stress and plastic viscosity values. The rheological properties were mainly controlled by the admixture type, followed by the type and content of clay and water-to-powder ratio (W/P). Empirical models were proposed to predict the rheology of earth-based paste, CEM, and SCEC mixtures using the governing key mixture parameters, including the fineness of the powder constituents (i.e., clay, silt, and cement), water content, EP thickness, paste volume, and packing of the granular skeleton.

Multiscale investigation of self-consolidating earthen materials using a novel concrete-equivalent mortar approach

Earth-based materials have been used since ancient times due to their low environmental impact and superior thermal performance. The rammed earth (RE) method, as a common earthen construction, consists in casting the material layer-by-layer, which is time-consuming, labor-intensive, and energy consuming. Designing self-consolidating earth concrete (SCEC) can speed up the construction process and overcome the disadvantages of conventional RE and enhance its performance. Achieving high fluidity and adequate compressive strength for early demolding is challenging because of the presence of clay and low cement content, respectively. Moreover, diversity of existing soil types does not allow to propose a universal mixture proportioning approach. In this study, workability, drying shrinkage, and compressive strength of SCEC mixtures were evaluated using a new concrete-equivalent mortar (CEM) approach to facilitate the optimization process and reduce the number of experiments and materials. The approach is mainly based on optimizing the excess paste (EP) thickness to consider the variation of packing density of the granular skeleton. The mixture parameters included the water-to-powder ratio (W/P), volumetric sand-to-total aggregate ratio (S/A), and the excess paste thickness. Good correlations between the investigated CEMs and their corresponding concrete mixtures were established. According to the carried-out ANOVA analysis, the main influencing parameters on workability, drying shrinkage, and compressive strength of SCEC include the specific surface area and Atterberg limits of the ternary binder system, W/P, paste volume, and EP thickness.

Using Natural Raw Materials and CEM Approach for the Design of Andean Volcanic Self-Compacting Concretes

Volcanic activity is characteristic of seismic zones. Consequently, volcanic material form part of the landscape in places where earthquakes are common natural phenomena. As volcanic wastes (VW) show pozzolanic activity, the substitution of manufactured Portland cement (PC) with VW is clearly a desirable option not only from an economical point of view but also to reduce the CO2 fingerprint. Therefore, designing concretes with volcanic Portland cements (VPC) clearly contributes to cleaner cement production. Construction and building activities in seismic zones need to use a specific kind of concrete—self-compacting concrete (SCC). The challenge we focused on was the design of SCC using VPC. The flow behavior of SCC is characterized by low yield stress, high plastic viscosity, and shear-thickening behavior at high shear. However, obtaining these striking properties of the concrete is not easy with traditional concrete flow tests (Abrams cone, etc.). Moreover, these methods are very costly in terms of time and material. An alternative that allows us to use absolute rheometry and which has been little explored consists in the substitution of concrete by an equivalent mortar. The so-named concrete equivalent mortar (CEM) approach was used in this study to obtain SCC formulations with VPC. Mini cone tests confirmed the absence of blend in some selected CEM formulations based upon the accomplishment of the criteria for SCC. Three concrete proposals were inferred from the respective CEM formulations. They adapted to the SCC European standard according to the Abrams cone spread test.

A method to increase the workability retention of concrete with limestone calcined clay based cementitious system using a dispersing agent containing sodium hexametaphosphate

This study is focused on increasing the workability retention of concrete with high replacements of cement by limestone calcined clay, or LC2 (≥45% by weight of binder). The effect of three commercially available PCE-based superplasticizers (SPs) on workability retention is studied. To enhance the retention ability of the concrete with SPs, a combination of sodium hexametaphosphate and anhydrous sodium carbonate as a dispersing agent (DA) is used. The study is conducted in three phases. In phase 1, the effect of DA with different SPs is studied on a concrete and concrete equivalent mortar with LC2 content of 45%. Flow table test and slump cone test are performed on mortar and concrete to assess the workability retention for 2 h from adding water to the mix. Additionally, the cube compressive strength is measured at 3, 7, and 28 days from casting. The addition of DA increases the workability retention of the concrete significantly. A slump of more than 200 mm is achieved after 2 h for concrete with DA against less than 100 mm without DA. Further, in phase 2, the effect of change in LC2 content on workability retention and compressive strength is studied. The LC2 contents used in this phase are 25, 35, 55, and 75%. It is observed that with an increase in the LC2 content, the workability retention drastically reduces for mortar mixes with only SPs. However, the addition of DA increased the workability retention of the mixes. The slump increased from 5 mm to 205 mm for a concrete mix with 75% LC2 content with addition of 0.5% DA. The last phase of the study is focused on evaluating the effect of SP and DA on the hydration kinetics of the mix by isothermal calorimetry. The combination of SP and DA acts as a strong retarder, resulting in a lower compressive strength at 3 days from casting. However, a minor reduction in compressive strength is seen at later ages with the addition of the DA. Further, a theoretical model is proposed elaborating the interaction of DA with the binder system, resulting in increased workability retention.

Unconventional tools for the study of the flow properties of concrete equivalent mortar based on recycled concrete aggregates.

The self-compacting concrete (SCC) mix design is much more complex than that of ordinary concrete. Increased testing on fresh concrete and a substantial volume of materials is consequently needed. The concrete equivalent mortar (CEM) method proposes an approach that simplifies and speeds up the experimental testing programmes. This paper seeks to establish the relationships between the rheological properties of SCC and the corresponding CEM mixes. Another aim is to validate the unconventional tools used to test the flow properties of CEM relative to the procedures applied for SCC. Different series of SCC and CEM mixes, based on natural and recycled aggregates, with various superplasticizer contents were tested. The flow behaviour of SCC was tested in line with procedures recommended by EFNARC; that of self-compacting concrete equivalent mortar (SC-CEM) was carried out with unconventional tools (mini-slump cone, slump flow time T250, mini L-Box, 2.5-mm sieve, and mini LCPC Box), described in detail in this paper. A rheometer equipped with vane geometry was also used to show the close relationship between SCC and the SC-CEM yield stress. The experimental results indicate that the fresh properties of the mixture series are congruent with the acceptance criteria of SCC, but they are affected when increasing the superplasticizer dosage and further impacted when recycled coarse aggregates (RCAs) replace natural coarse aggregates (NCAs). The slump flow test appears to be a good practical means for predicting the yield stress of SC-CEM. The cross-referencing results reveal significant relationships between SCC and the corresponding SC-CEM, particularly for filling ability and passing properties. Reasonable correlation coefficients from 0.70 to 0.85 were found.

Effect of Crack Width, Density, and Depth on Strength and Durability of Concrete-Equivalent Mortar

Effect of Crack Width, Density, and Depth on Strength and Durability of Concrete-Equivalent Mortar

Influence of temperature on the rheological behaviour of eco-mortar with binary and ternary cementitious blends of natural pozzolana and marble powder

With the advent of new concrete such as low-impact environmental concrete, and the new implementation techniques of cementitious materials such as 3D printing and pumping, it becomes crucial to control the rheological behaviour of these materials taking into account the different climatic conditions. The main objective of this study is to investigate the influence of mineral additions and temperature on the rheological parameters (yield stress, plastic viscosity) and the fresh properties (slump, flow time) of low-impact environmental concrete using concrete-equivalent mortar (CEM) concept. For this purpose, fifteen mixtures of CEM were prepared by substituting the cement with natural pozzolana (PZ) and marble powder (MP) in binary and ternary blend systems. The rheological and fresh properties of CEM mixtures were investigated at different temperatures ranging from 10 °C to 50 °C. The results obtained revealed that, the use of binary and ternary blended cements based on PZ and MP increased the fresh properties and decreased the rheological parameters of CEM tested in a standard environment of temperature 20 °C. In addition, the increase in temperature affected negatively the fresh properties and rheological parameters of all binary mixtures. However, at low temperature (10 °C), the viscosity and yield stress of ternary mixtures have been enhanced.

Effect of temperature on early-age properties of self-consolidating concrete equivalent mortar

In this study, the effect of material temperature during casting on fresh properties, hydration kinetics, and early-age compressive strength of self-consolidating concrete (SCC) was evaluated. Concrete equivalent mortars (CEMs) based on SCC mixture designs with water-to-binder ratios of 0.41 and 0.45 were investigated. The SCC mixtures are targeted for infrastructure and building construction and precast applications. The CEMs were prepared at temperatures ranging from 8 to 36°C. Superplasticizer (SP) and air-entraining agent (AEA) demand were evaluated for the CEM mixtures made with different supplementary cementing material (SCM) and limestone filler types. Test results showed that the ambient temperature can significantly affect the SP and AEA demand, hydration kinetics, and compressive strength after 1 d of age. According to the ultraviolet–visible spectrophotometry (UV/Vis) test, the absorption rate of polycarboxylate-based SP decreased with temperature. In contrast, the sensitivity of polynaphthalene sulfonate-based SP to temperature was minimal. Relationships between the variations of different admixture contents, heat flux, and compressive strength with temperature were developed. For a constant slump flow and air content, the demand of the SP and AEA, heat flux, and 1-d compressive strength of CEMs increased linearly with material temperature.

Coupled Effect of temperature and additions on the rheological behavior of concrete equivalent mortars (CEM)

The aim of this work is to study the influence of mineral additions on the rheological behavior of low impact environmental concrete with its concrete equivalent mortar (CEM) at different temperatures.The experimental study is carried out on cement-based CEM substituted by two additions namely, natural pozzolana (PZ) and marble powder (PM), with a substitution rate of 5 to 20%, a ratio of water on binder E / L = 0.5 and a percentage of superplasticizer based on polycarboxylates SP = 0.30%. The rheological parameters, the workability and the flow time of the mixtures were tested by a coaxial rheometer, a mini cone and the LCPC maniabilitimetre respectively at 10 ° C, 20 ° C and 30 ° C. The results show that the substitution of cement by natural pozzolana and marble powder in binary system generally improved viscosity and yield stress at 20°C and 30°C, while at 10°C natural pozzolana negatively affected the rheological parameters and workability.

Do the geometry and aggregates size influence external sulfate attack mechanism?

ESA performance testing protocols are mainly a set of exposure conditions, monitoring strategy, and specimens configuration. Although the large feedback on the representativeness of exposure conditions and the relevance of monitored parameters, the effect of specimen configuration still deserved to be studied. In order to investigate the effect of composition and geometry on ESA degradation progress and performance evaluation, an experimental campaign was conducted in this study. Among the 8 tested specimen configurations, 5 geometries (prismatic, cylindrical and 3 hollow cylindrical geometries) and 3 compositions (concrete, concrete equivalent mortar and standard mortar), the cylindrical mortar specimen was selected as the most adapted configuration, in term of ESA degradation expression, for the adopted performance testing procedure. The different configurations lead to the same overall mechanism of degradation but the geometry and the composition influenced the magnitude of some chemical or physical degradation parameters, due to couplings between chemical and mechanical degradation.

Fresh behavior of mortar based on recycled sand – Influence of moisture condition

Recycled Concrete Aggregates (RCA) are composed of a mixture of natural aggregates more or less coated by hardened cement paste. The latter has a high capacity of water absorption. In concrete, amount of water present in the cement paste, excluding the water absorbed by aggregates, (called effective water – Weff) strongly influences the fresh and hardened properties of the material. This amount of water is highly dependent on the water absorbed by the aggregates during mixing, particularly for very porous aggregates which possess large water absorption as RCA. However, the amount of water absorbed depends itself on the initial state of saturation of aggregates. The aim of this work is firstly to measure the water absorption coefficient of recycled sand (RS) by different methods, then to study the influence of moisture condition of RS on the fresh behavior of mortar. Standard (EN 1097-6) and non-standard (IFSTTAR N°78, Extrapolation) methods are used in this work to measure the water absorption of RS. The results show that the water absorption closely depends on the experimental protocol used. The workability of mortars containing RS prepared in different saturation states is then measured with the Concrete Equivalent Mortar (CEM) cone. We show that initial water content, pre-saturation method and pre-saturation time significantly influence the initial workability of mortars.

New insight into the equivalent concrete mortar approach for self-consolidating concrete

The concrete equivalent mortar (CEM) approach consists in replacing the coarse aggregates (CA) of concrete by a mass of sand to provide an equivalent specific surface area at mortar scale. Such approach can be used to reduce time and cost needed to design self-consolidating concrete (SCC). The approach is extended with less success to evaluate rheological properties of SCC using those of the corresponding CEM. The limitation of the approach is mainly due to the fact that the surface area of aggregates is the only used criterion. The objective of this investigation is to evaluate the applicability of the original CEM approach and establish correlations between rheological properties of CEM and SCC. Various SCC mixtures were proportioned with different CAs and binder contents varying from 27 to 36% and 300 to 500 kg/m3, respectively. The obtained test results show that the excess paste theory is a key factor in studying relationship between CEM and SCC. Good correlations between flow properties of CEM and SCC are obtained when the excess paste thickness and CA content are taken into account.

Paste and mortar studies on the influence of mix design parameters on autogenous shrinkage of self-compacting concrete

By means of the concrete equivalent mortar (CEM) principle, concrete properties can be experimentally studied at mortar level. Based on this principle, the objective of this paper is to study the influence of mix design parameters on autogenous shrinkage of self-compacting concrete by means of tests at mortar level. Furthermore, autogenous shrinkage tests have been performed at paste level, enabling to study the correlation between shrinkage of paste and mortar. For limestone filler based self-compacting concrete, the obtained experimental results indicate that autogenous shrinkage is increasing with decreasing fines/cement ratio (A/C), although the influence of A/C is not as important as the influence of water/cement ratio (W/C). Furthermore, based on mortar and paste results, it is shown that the model developed by Le Roy, describing the influence of aggregate properties and contents on shrinkage of cementitious materials, is also valid for the autogenous shrinkage of limestone filler based self-compacting cementitious materials.

Rheology of concrete: a study case based upon the use of the concrete equivalent mortar

A deeper and wider knowledge of the rheology of concrete could be obtained if a variety of absolute rheological parameters were measured. Although a valuable rheological classification can be induced from concrete rheometers, they do not give the same absolute values of the rheological parameters. Moreover, rheological tests with concrete require a large volume of material. The aim of this work is to use the concrete equivalent mortar (CEM) method (Schwartzentruber and Catherine, Mater Struct 33:475–482, 2000) to get concrete rheological information with an absolute rheometer. Additionally some graph tools that resume the results from several rheological tests are suggested for the design of concretes. CEM have been formulated to test concrete formulations with an absolute rheometer. Steady flow measurements of a CEM corresponding to a self-compacting concrete (SCC) clearly reveal characteristic non-linear viscoplastic behavior which it is not shown by conventional tests used to characterize concretes. The thixotropic behavior of a concrete is well-established using three different rheological tests that can be made with an absolute rheometer testing its corresponding CEM. These tests reveal aspects of the strength and kinetics of the micro-structure that are not observable when thixotropy of concrete is semiquantified with conventional methods. Only with a CEM is possible to make oscillatory shear tests. In this way the viscoelastic behavior of the concrete can be characterized. Results of practical interest are so obtained. For example, the necessity of vibration at rest application to the fresh concrete can be established from frequency sweep tests of CEM in the linear viscoelastic region. The correlation between rheological behaviors of a concrete and its corresponding CEM has been supported. Steady flow and thixotropy rheographs of CEM are suggested as tools for an easy and fast determination of adequate formulation for specific applications.

Use of CEM Approach to Develop and Optimize High-Performance Underwater Concrete

The development and optimization of underwater concrete (UWC) characteristics (i.e., washout loss, threshold water head prior to concrete deterioration, and residual compressive strength) require considerable time, effort, and energy for testing. This paper seeks to propose a new testing method developed on the basis of the concrete-equivalent-mortar (CEM) approach to optimize and simplify evaluating the effect of mixture composition on washout characteristics of UWC cast under different conditions. Washout of CEM was determined using an adapted version of the commonly used CRD C61 test method as well as by simulation using an air-pressurized tube measuring 300 mm in height. Test results showed that CEM mixtures proportioned without coarse aggregates can adequately be used to predict washout characteristics of UWC. Statistical regression models were developed to enable direct estimation of washout loss and threshold water head of CEM and UWC mixtures.

Surface settlement of cementitious-based materials determined by oedometer testing

The oedometer test is commonly used in soil mechanics to evaluate consolidation of clays and other compressible soils. A research project was undertaken to evaluate the suitability of such test to assess surface settlement of freshly mixed cementitious-based materials. Three series of concrete-equivalent-mortar (CEM) mixtures made with different cement contents, water-to-cementitious materials ratio (w/cm), silica fume, and viscosity-modifying admixture (VMA) were tested. Validation of test results was performed by casting concrete mixtures in a PVC column having 600-mm height and 200-mm diameter. Test results have shown that CEM settlements determined using the oedometer test as well as concrete settlements determined using the 600-mm PVC column are affected quite similarly by the mixture composition. For example, for given consistency, settlement decreases with the increase in cement content, decrease in w/cm, and incorporation of increased concentrations of silica fume or VMA. Statistical analysis was then performed to propose regression models for predicting maximum settlement of concrete through the determination of CEM characteristics.

Influence of aggregate size on the mechanical and transport properties of concretes and concrete-equivalent mortars

In this study, the influence of the aggregate size on the mechanical and transport properties of concrete and concrete-equivalent mortars is investigated. A concrete mixture was proportioned having a water–cement ratio of 0.45 and a cement content of 450 kg/m3 with a maximum aggregate size of 22.4 mm. Then, keeping the total aggregate surface area constant, three mixtures were proportioned with the same water–cement ratio, but the maximum aggregate size decreased to 16, 8, and 4 mm using the concrete-equivalent mortar method. Mechanical properties including compressive strength, splitting tensile strength and transport properties including rapid chloride permeability, water sorptivity, water absorption, and water permeability tests were performed at 7 and 28 d. Test results revealed that decreasing the maximum aggregate size increased the water permeability, rapid chloride permeability, water absorption, and sorptivity values, but decreased the compressive and split tensile strengths of concrete and concrete-equivalent mortars.