Cement Mortar Specimens Research Articles

Experimental and numerical analysis of 3D printed cement mortar specimens using inkjet 3DP

Investigations involving the experimental and numerical analysis of inkjet (powder-based) 3DP are relatively limited for cement mortar materials. This study, by using cement mortar specimens, aimed to determine the optimum strength of 3D printed structural members in all three planes by identifying the compressive strength of cubes, the modulus of elasticity and Poisson’s ratio. In addition, this study aimed to analyse and verify the numerical model for 3D printed cementitious mortar (CP) prisms and beams using an inkjet 3D printer by considering the mechanical behaviour of the printed prisms under compression. Robust and optimal mechanical properties of the 3D printed cementitious mortar obtained from laboratory testing were utilised in the simulation of structural components using ABAQUS software. As inputs for simulation, the strength properties of the printed objects in all three cartesian planes were obtained from test results. The obtained results showed that the printed cementitious materials have orthotropic properties and that the results of experiments were consistent with the analytical solutions and hypothesised model for the different geometric shapes. This finding is extremely valuable in determining the optimum features of 3D printed structures.

Detecting cracks due to steel corrosion in reinforced cement mortar using intermodulation generation of ultrasonic waves

It has been studied the sensitivity of the technique of intermodulation of ultrasonic waves to detect different damage states of concrete due to embedded steel corrosion. Accelerated corrosion tests have been conducted on reinforced cement mortar specimens, while monitoring the appearance and width evolution of visible surface cracks and performing intermodulation measurements. It has been established a statistically acceptable “upper control limit” for the initial (undamaged) Intensity Modulation Ratio (R) values. After subjecting the samples to the corrosion tests, it was observed that the greater the degree of damage, the higher the value ranges and the variability degree of R.

Phosphorus recovery from incinerated sewage sludge ash (ISSA) and reutilization of residues for sludge pretreated by different conditioners

• Effect of different sludge conditioners on P recovery from ISSA was first studied. • Fe and Ca elements in sludge conditioner influenced the P speciation in ISSA. • Higher Ca content in ISSA resulted in lower P leaching efficiency. • Heavy metals mainly existed in residual specie with low mobility risk in ISSA. • Acid-leaching residue of ISSA could be reused as cement mortar additives. Phosphorus (P) recovery from incinerated sewage sludge ash (ISSA) has attracted increasing attentions in recent years. In this study, the P recovery was comparatively investigated on two types of ISSA for sewage sludge pretreated by Fenton's reagent, and a composite conditioner of Fenton's reagent and lime (referred to as ISSA-F and ISSA-FL, respectively). ISSA derived from raw sludge (referred to as ISSA-RS) was studied as the control group. The P species results showed that the proportions of AP (Ca-bound P) and NAIP (Al/Fe-bound P) in the ISSA samples were significantly affected by the added Fe and Ca elements in the sludge conditioner. The order of leaching efficiency of P in different ISSA samples was ISSA-F (100%) > ISSA-RS (94.4%) > ISSA-FL (83.1%), which was significantly related to the Ca content in those ISSA samples. Higher Ca content in the ISSA-RS and ISS-FL samples induced calcium oxalate precipitation during leaching process, which hindered the release of P from ISSA. P recovery product mainly composed of aluminum hydroxyphosphate was prepared from the purified solutions leached from different ISSA samples. Moreover, acid-leaching residues of different ISSA samples after P recovery were proposed to be reutilized as cement mortar additives by replacing 15 wt% of cement. The mechanical strength of the test cement mortar specimens with acid-leaching residues was comparable to that of the control cement mortar specimen without residue.

An Innovative Approach to Simulate Biocorrosion in Concrete Pipes

Abstract Concrete corrosion in wastewater concrete pipes is mainly caused by the diffusion of aggressive solutions and in situ production of sulfuric acid by sulfur oxidizing microorganisms, which affect the physicochemical properties of concrete. In this study, a novel pilot-scale experimental setup was designed to replicate conditions in sewage systems as well as the bacterial-induced corrosion process in concrete pipes. The reliability of this test was evaluated by conducting a flexural strength test on arch-shaped cement mortar specimens over a 6-month period. Quantitative assessments of the properties were carried out over the 6-month period, and the average corrosion rate of 3 mm/y with 73 % reduction in bending strength (of the initial strength) and an average weight loss of 15 % was observed in cement-based mortar specimens. The proposed methodology and the results provide a better understanding of the biocorrosion process and quantitative information on the performance and effectiveness of different pipe/coating materials, which is necessary in evaluating concrete pipe’s durability.

Non-Extensive Statistical Analysis of Acoustic Emissions: The Variability of Entropic Index q during Loading of Brittle Materials until Fracture.

Non-extensive statistical mechanics (NESM), introduced by Tsallis based on the principle of non-additive entropy, is a generalisation of the Boltzmann–Gibbs statistics. NESM has been shown to provide the necessary theoretical and analytical implementation for studying complex systems such as the fracture mechanisms and crack evolution processes that occur in mechanically loaded specimens of brittle materials. In the current work, acoustic emission (AE) data recorded when marble and cement mortar specimens were subjected to three distinct loading protocols until fracture, are discussed in the context of NESM. The NESM analysis showed that the cumulative distribution functions of the AE interevent times (i.e., the time interval between successive AE hits) follow a q-exponential function. For each examined specimen, the corresponding Tsallis entropic q-indices and the parameters βq and were calculated. The entropic index shows a systematic behaviour strongly related to the various stages of the implemented loading protocols for all the examined specimens. Results seem to support the idea of using the entropic index as a potential pre-failure indicator for the impending catastrophic fracture of the mechanically loaded specimens.

Effect of High-Dispersible Graphene on the Strength and Durability of Cement Mortars

Graphene’s outstanding properties make it a potential material for reinforced cementitious composites. However, its shortcomings, such as easy agglomeration and poor dispersion, severely restrict its application in cementitious materials. In this paper, a highly dispersible graphene (TiO2-RGO) with better dispersibility compared with graphene oxide (GO) is obtained through improvement of the graphene preparation method. In this study, both GO and TiO2-RGO can improve the pore size distribution of cement mortars. According to the results of the mercury intrusion porosity (MIP) test, the porosity of cement mortar mixed with GO and TiO2-RGO was reduced by 26% and 40%, respectively, relative to ordinary cement mortar specimens. However, the TiO2-RGO cement mortars showed better pore size distribution and porosity than GO cement mortars. Comparative tests on the strength and durability of ordinary cement mortars, GO cement mortars, and TiO2-RGO cement mortars were conducted, and it was found that with the same amount of TiO2-RGO and GO, the TiO2-RGO cement mortars have nearly twice the strength of GO cement mortars. In addition, it has far higher durability, such as impermeability and chloride ion penetration resistance, than GO cement mortars. These results indicate that TiO2-RGO prepared by titanium dioxide (TiO2) intercalation can better improve the strength and durability performance of cement mortars compared to GO.

Utilization of Upgraded Recycled Concrete Aggregates and Recycled Concrete Fines in Cement Mortars

Waste concrete is the most predominant constituent material among construction and demolition waste. Current waste concrete recycling is limited to the use of recycled concrete aggregates as a road-base material and less as aggregates in new concrete mixes. Further, the production of recycled concrete aggregates results in the generation of a high amount of fines, consisting mainly of cement paste particles. Hence, this study aims to produce the cement mortars using the upgraded recycled concrete aggregates (sand granulometry) for the total replacement of natural aggregates and recycled concrete fines activated through a thermal treatment method as a partial cement substitution material. Cement mortar specimens were tested for their compressive and flexural strength, density and water absorption performance. The results showed that the combined usage of upgraded recycled concrete sand for total replacement of primary crushed sand and recycled concrete fines as partial cement replacement material is a promising option to produce cement mortars.

Experimental investigation into graphene’s effects on the mechanical properties of cement mortar under specific sonication parameters

Graphene and its derivatives have been studied as nanomaterials in many different fields owing to their various interesting properties. Many researchers have investigated the mechanical properties of different graphene cementitious composites, and the current study investigates the effect on the mechanical properties of cement mortar of adding graphene with and without the use of an ultrasonic homogeniser. To examine this effect, all other testing conditions and requirements such as mix design content, mixing procedure, curing time, specimen size and sonication parameters were maintained at the same levels across tests. Cement mortar specimens containing different percentages of graphene (0, 0.003, 0.006, 0.009, 0.012 and 0.03% by weight of cement) were experimentally tested after 7 and 28 days to determine the effect of graphene dosage on their quasi-static strengths. The results showed an obvious enhancement in both compressive and flexural strengths after adding each graphene dosage to the mix without sonication; the compressive strength was increased by 12% with a 0.006% dose of graphene and the flexural strength was increased by 27% at a 0.009% dose of graphene. On using the sonicator at the specified parameters, the compressive strength increased by 33% for the 0.006% dose of graphene, offering an increment of 20% in strength due to the sonication effect; however, there was no noticeable effect on the flexural strength.

The Deterioration of Cement Mortar under the Coupled Conditions of Stray Current and Sulfate

Abstract Subway engineering often suffers varieties of corroding environments. This article investigated the effects of stray current and external sulfate coupled conditions on the deterioration of cement mortar. The cement mortar specimens suffered from one-dimensional sulfate attack. Simultaneously, a direct current electric field was applied to both ends of the specimen to simulate stray current. By contrast, a group of mortar specimens was immersed in the same concentration of sodium sulfate (Na2SO4) solution. In order to investigate the effect of stray current on the sulfate attack of cement mortar, the compressive strength of specimens was tested. In addition, the sulfate ions profile in the cement mortar specimen was tested. Corrosion products and the microstructure of specimens were investigated using x-ray diffraction, Fourier-transform infrared spectroscopy, and scanning electron microscope. Experimental results showed that stray current could exacerbate strength degradation and accelerate the sulfate ions’ migration into the cement mortar, which led to the number of total sulfate ions and free sulfate ions at the same depth being higher than that of the immersion group, and quantities of corrosion products (gypsum and ettringite) were also higher than those of the immersion group. In a word, the stray current aggravated the sulfate attack of cement mortar. Therefore, the durability of cement mortar exposed to the stray current and sulfate coupled conditions should be given more attention.

Experimental study of the addition of oil palm mesocarp fiber on the physical and mechanical properties of fiber cement mortar composites

Composite materials based on natural fibers are increasing in demand in various sectors of industry because of their interesting specific properties. This work is a contribution to the valorization, of plant fibers from agricultural plantations in Cameroon, in fiber cement mortar (FCM). This paper studies the influence of the addition of oil palm mesocarp fiber (OPMF) on the physical (water absorption, density and compactness) and mechanical (compressive strength and flexural strength) properties of cement mortars. The fibers used in this paper are extracted from oil palm mesocarp (palm kernel pulp) by a mechanical and manual process. Cement mortar specimens were then made with different proportions of fibers: 0% (reference mortar), 1%, 2%, 3% and 3.5% fibers. Physical and mechanical tests are then carried out on our specimens. Regardless of the duration of immersion in water, the results show that the water absorption rate increases with a greater amount of fiber in the FCM specimens. On the other hand, an inverse effect is observed on density, which decreases from 2277.5 (samples with 0% fiber) to 942.1 kg/m3 (samples with 3.5% fiber) for apparent density and from 2641.2 to 1945.7 kg/m3 for absolute density. On the mechanical properties, there is a steady decrease in compressive strength from 42.47 (for the reference mortar at 0% fiber) to 31.1 MPa (for the sample at 3.5% fiber). In bending, there is first an increase and then a decrease in strength with the amount of fibers. The maximum flexural strength is obtained for a 2% fiber composition. The FCM has a better strength/density ratio. Finally, the addition of OPMF, in small proportion in the cement mortar, allows a lightening of the structure, but induces a small decrease in mechanical resistance. Our FCM can be used in the manufacture of cinderblocks or as internal wall roughcoating mortar.

Application of novel synthesized nanocomposites containing κ-carrageenan/PVA/eggshell in cement mortars

This study is a preliminary attempt to present the preparation and the first time a κ-carrageenan/PVA/eggshell nanostructure is used as a novel biodegradable and homogeneous nanostructure in cement composition. In order to clearly understand the effects these additives have on the mechanical properties of cementitious composites, they were synthesized in double and triple combinations and added into mortar mixtures. Three different cement mortar specimens were prepared by integrating the additives in ratios of 0, 0.1, 0.5 and 1% by cement weight and flexural and compressive strengths of the specimens were determined at the ages of 7 and 28 days. The flowability of the presented nanostructures was also discussed. The results revealed a 10–11% increase in both compressive and flexural strengths for the specimens prepared with the triple combination of the proposed additives. Moreover, strain capacity was enhanced as a result of the efficient dispersion of additives in the cement matrix.

Criticality Hidden in Acoustic Emissions and in Changing Electrical Resistance during Fracture of Rocks and Cement-Based Materials.

Acoustic emissions (AE) due to microcracking in solid materials permit the monitoring of fracture processes and the study of failure dynamics. As an alternative method of integrity assessment, measurements of electrical resistance can be used as well. In the literature, however, many studies connect the notion of criticality with AE originating from the fracture, but not with the changes in the electrical properties of materials. In order to further investigate the possible critical behavior of fracture processes in rocks and cement-based materials, we apply natural time (NT) analysis to the time series of AE and resistance measurements, recorded during fracture experiments on cement mortar (CM) and Luserna stone (LS) specimens. The NT analysis indicates that criticality in terms of electrical resistance changes systematically precedes AE criticality for all investigated specimens. The observed greater unpredictability of the CM fracture behavior with respect to LS could be ascribed to the different degree of material homogeneity, since LS (heterogeneous material) expectedly offers more abundant and more easily identifiable fracture precursors than CM (homogenous material). Non-uniqueness of the critical point by varying the detection threshold of cracking events is apparently due to finite size effects which introduce deviations from the self-similarity.

Similarity of fluctuations in critical systems: Acoustic emissions observed before fracture

Here, we study the scaled distributions for the variance κ1 of natural time χ when analysing the energy time-series of acoustic emission recorded when marble and cement mortar specimens were subjected to mechanical loading until fracture. It is shown that the κ1 scaled distributions exhibit – for at least three orders of magnitude – a characteristic exponential tail like that previously found for the order parameter in equilibrium (e.g., two-dimensional Ising model), and in non-equilibrium (e.g., turbulent flow) critical systems as well as in seismicity. The presented findings, which are also compared to those coming from the non-conservative Olami–Feder–Christensen earthquake model and the Burridge–Knopoff train model, advocate for the use of κ1 as an order parameter for the acoustic events preceding failure in a fashion similar to that in the case of seismicity.

Microstructural Changes in Concrete: Postfire Scenario

The thermal and mechanical properties of coarse aggregates, cement mortar, and cement concrete specimens of varying mix proportions were studied after exposure to a range of high temperatures. For the tests, 70.6-mm mortar cubes, concrete cubes of 100 and 150 mm, and concrete cylinders of 100 and 150 mm diameters and 200 and 300 mm heights, respectively, were cast. The water to binder ratio was varied from 0.35 to 0.5. These specimens were exposed to a wide range of temperatures varying from room temperature (24°C±2°C) to 1,000°C and tested to understand the degradation in strength and spalling behavior of normal-strength concrete (NSC) and high-strength concrete (HSC). The crack initiation and propagation was studied using micrographs obtained from scanning electron microscopy (SEM). Changes in the porosity of coarse aggregates and concrete at elevated temperatures is quantified by incorporating digital image processing on the SEM micrographs. The influence of high temperature on the physical and chemical properties of concrete and concrete constituents at the macroscale and microscale are discussed. Simple empirical relationships to compute residual compressive strength of NSC and HSC at elevated temperatures are proposed. It is concluded from the results that the degradation in the concrete strength at high temperatures is primarily a result of nonuniform thermal expansion of concrete and its individual constituents leading to porosity changes in the cement–sand matrix, coarse aggregates, and interface between the two.

Synthesis and self-healing properties of composite microcapsule based on sodium alginate/melamine-phenol–formaldehyde resin

In view of the inevitable microcracks and local damage of concrete materials, a new type of self-healing microcapsule material was proposed. The SA/MPF-E44 composite microcapsule material with sodium alginate/melamine phenolic resin as the shell and epoxy resin as the core was prepared by in situ polymerization. The surface morphology of the microcapsules was observed by optical microscope and scanning electron microscope. The particle size analysis was performed using a Malvern analyzer. By performing Fourier transform infrared spectrometry and a differential scanning calorimetry analysis, the functional group changes and thermal stability of the composite microcapsules were studied. The compression resistance and repair performance of cement mortar specimens with different dosage of microcapsules were tested by a uniaxial compression experiment. It can be concluded that the composite microcapsules have the characteristics of a small particle size, and the coverage rate has increased significantly. The average particle diameter is approximately 55.24 μm, and the coating ratio is 64.93%. When the microcapsule content is 4%, the microcapsule has the best compression and repair performance. The self-healing behavior of the epoxy resin and curing agent in cracks was studied by a molecular dynamics simulation. Finally, it is shown that SA/MPF composite microcapsules have certain advantages in cost and eco-efficiency, and have good self-healing ability for microcracks in concrete materials.

Simulation and Recognition of Concrete Lining Infiltration Degree via an Indoor Experiment

It is difficult to form a method for recognizing the degree of infiltration of a tunnel lining. To solve this problem, we propose a recognition method by using a deep convolutional neural network. We carry out laboratory tests, prepare cement mortar specimens with different saturation levels, simulate different degrees of infiltration of tunnel concrete linings, and establish an infrared thermal image data set with different degrees of infiltration. Then, based on a deep learning method, the data set is trained using the Faster R-CNN+ResNet101 network, and a recognition model is established. The experiments show that the recognition model established by the deep learning method can be used to select cement mortar specimens with different degrees of infiltration by using an accurately minimized rectangular outer frame. This model shows that the classification recognition model for tunnel concrete lining infiltration established by the indoor experimental method has high recognition accuracy.

Mechanical properties of blended cement mortar systems exposed to ammonium chloride environment

There are number of areas where cement composites can be exposed to ammonium based compounds such as agricultural land, chemical fertilizer plants, waste waters, polluted and industrial environments, which can induce severe and premature deterioration of concrete systems. Based on the review of literature, the most common and deleterious ammonium based salts were found to be ammonium nitrate, ammonium chloride and ammonium sulphate. The cementitious systems with Ordinary Portland Cement (OPC) may be attacked easily by these ammonium based chemicals as the OPC hydrates such as Portlandite and C-S-H gel are considered to be unstable in these aggressive media. Thus, it is necessary to understand the alteration kinetics of cementitious systems and the effectiveness of Supplementary Cementitious Materials (SCMs) in improving the resistance when exposed to ammonium based environments for develpoing more durable and sustainable concrete systems. The aim of this experimental study was to investigate the durability aspects in terms of the changes in mechanical properties of cement mortar specimens made with OPC and different combinations of various Supplementary Cementitious Materials (SCMs) exposed to ammonium based salt solution prepared using chemical grade ammonium chloride (NH4Cl). The mortar specimens were exposed to ammonium chloride solution in two different concentrations (1.25 M and 2.5 M) for a maximum exposure duration of two and half months. The SCMs used for the study include Class F Fly ash (FA), Ground Granulated Blast Furnace Slag (GGBS), and Silica fume (SF). The changes in the mechanical properties were evaluated on the basis of visual assessment, depth of penetration, changes in the compressive strength, changes in Ultrasonic Pulse Velocity (UPV) and relative dynamic modulus of elasticity. From all the test results, it can be concluded that the ternary blended mix with OPC, GGBS and Silica fume (OPC-GGBS-SF) has higher resistance to ammonium chloride attack. The results stress the need to include SCMs and the importance to tailor make the concrete for structures exposed to aggressive environment like ammonium chloride.

A study on flexural behavior of geopolymer mortar based ferrocement

Abstract The aim of this work is to investigate the presence of ferrocement mesh in geopolymer mortar and the obtained results are compared with cement mortar prisms. GGBS and class F Fly ash are used as binders in geopolymer mortar and the alkaline activator solution (sodium hydroxide + sodium silicate) with 8 M sodium hydroxide solution having an alkaline modulus (Na20/SiO2) of 0.6 is used. Three different mixes i.e., Binder: Fine aggregate ratio of 1:1, 1:1.5, 1:2 and different layers of wire mesh (i.e., 0layers, 1layer, 2layers, 3layers) were considered in this study. Prisms of size 500 mm*100 mm*25 mm and cubes of size 100 mm*100 mm*100 mm were cast with cement mortar and geopolymer mortar. The obtained results indicate that increase in layers of wire mesh had a positive effect on flexural strength and toughness. Both cement mortar and geopolymer mortar specimens showed nearly same flexural strength when more layers of wire mesh are present.

Use of Higher-Harmonic and Intermodulation Generation of Ultrasonic Waves to Detecting Cracks due to Steel Corrosion in Reinforced Cement Mortar

The aim of this work was to provide further confirmation of the possible use of non-linear ultrasonic techniques for detecting the cracking due to corrosion of steel reinforcements in concrete. To this end accelerated steel corrosion tests have been conducted on model reinforced cement mortar specimens, while monitoring the appearance and width evolution of visible surface cracks, and performing non-linear ultrasonic measurements based on the phenomena of harmonic distortion and intermodulation. A new parameter, based on the difference between the amplitude of the fundamental frequency and the sum of the amplitudes of all the first-order and second-order intermodulation products, has been proposed in this work. The results confirm that the appearance of visible surface micro-cracks are preceded and accompanied by the observation of strong non-linear features in the received signal. Furthermore, the new parameter proposed in this work is as efficient as the relative non-linearity parameters, classically used in harmonic distortion non-linear ultrasonic studies, for detecting the non-linear features associated with the critical events of the cracking of cement mortar due to embedded steel corrosion. A hypothesis has been developed considering the possible effect of the filling of the void space by liquid containing rust products after the formation of new cracks or the enlargement of its width. This filling process, which might be particularly enhanced by net convective transport of liquid, would explain the evolution of the values of all the parameters used for putting in evidence the non-linear elastic features after the critical events of the cracking process.

Non-Extensive Statistical Analysis of Acoustic Emissions Recorded in Marble and Cement Mortar Specimens Under Mechanical Load Until Fracture.

Non-extensive statistical mechanics (NESM), which is a generalization of the traditional Boltzmann-Gibbs statistics, constitutes a theoretical and analytical tool for investigating the irreversible damage evolution processes and fracture mechanisms occurring when materials are subjected to mechanical loading. In this study, NESM is used for the analysis of the acoustic emission (AE) events recorded when marble and cement mortar specimens were subjected to mechanical loading until fracture. In total, AE data originating from four distinct loading protocols are presented. The cumulative distribution of inter-event times (time interval between two consecutive AE events) and the inter-event distances (three-dimensional Euclidian distance between the centers of successive AE events) were examined under the above concept and it was found that NESM is suitable to detect criticality under the terms of mechanical status of a material. This was conducted by evaluating the fitting results of the q-exponential function and the corresponding q-indices of Tsallis entropy and , along with the parameters and . Results support that for AE data recorded from marble and cement mortar specimens of this work, which is in good agreement with the conjecture previously found in seismological data and AE data recorded from Basalt specimens.