mortar

Grading is one of the most important characteristics of cement, which has a great impact on its performance in fresh and hardened concrete. The most common methods of cement grading monitoring are determination of residue through 200, 90 and 45 micron sieves, fineness test by Blaine method and Laser Grading. Combining the results of these tests is the best way to control cement grading. In this study, it was tried to introduce the main indices of cement grading and its effect and suitale ranges. Therefore, through a laboratory operation, 204 samples of type 2 Portland cement were prepared and their physical characteristics were determined and laser grading was done. Then, by making concrete mixtures with constant workability (slump 8±0.5 cm), the performance of cement samples with various grading in concrete mixtures was investigated. Among the most important results in this extensive study, the clear effect of increasing the amount of 3-30 micron particles and the uniformity coefficient of cement on the compressive strength of concrete and mortar and the presenting of the relationships can be mentioned.The compressive strength of 28-day standard mortar is approximately equal to half of the amount of 3-30 micron particles and constant value o 22 MPa.

In most buildings, concrete and steel are used side by side, and according to the type of loads, various stresses are created at their interface. When the repair layer is in direct contact with the steel or reinforcement, the stresses caused by the shrinkage of the mortars as well as temperature changes have a negative effect on the adhesion between the repair mortar and the steel. According to the CEB-FIP MODEL CODE standard, the shear adhesion between mortar and simple reinforcement is equal to τ=0.3√(fc). But it has not provided conditions to consider the type of implementation. Considering that shrinkage causes shear stresses at the interface of mortar and steel, therefore, in this article, by using the in-situ twist-off test, the shear adhesion strength between mortar and plain steel has been evaluated under different processing conditions. The results of the twist-off test show that the above equation is used if the sample is under processing until the moment of the test, otherwise there will be a big drop in the amount of adhesion, which even reaches 50%. The results of the shear adhesion strength obtained from the twist-off test for the samples that were processed in water until the time of the test, at a young age are almost equal to the equation provided by the CEB-FIP Model Code standard. At older ages, the shear bond strength results from the twist-off test between mortar and steel are on average more than 10% higher than the equation provided by the CEB-FIP Model Code standard. For the samples that were processed for a week and then left in the open space, it is observed that there is a big difference between the shear adhesion strength obtained from the twist-off test and the equation provided by the CEB-FIP Model Code standard. For practical cases where processing is usually done for about seven days, it is suggested that the shear adhesion strength between steel and mortar is measured for samples that have been subjected to wet processing for at least one week and prepared and stored under appropriate conditions. According to the equation, τ=0.15√(fc) should be considered. The amount of 90-day shrinkage for mortar treated in water and left in open space is 0.1083 and 0.2679%, respectively. The amount of shrinkage for mortar processed in water is 59% less than the shrinkage of mortar left in the open space.

Mortars are heterogeneous construction materials whose raw materials, manufacturing processes and application conditions have continuously evolved throughout time . Mortars are artificial construction materials that consist of; one or more mineral adhesives whose main function is to connect loose grains using different chemical changes in their mass, aggregates that are used to create volume stability on the mortar mass and water that is used to mix the mortar components into a sticky dough. Materials must be carefully measured and mixed to give the desired balance to bring out its essential properties. Therefore, in this research, 11 mixing plans for mortar, which is a kind of reactive powder concrete, with sand to cement ratios of 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 25 6.5, 6.5, 6.75, and 7 were made and the effect of increasing the ratio of sand to cement was evaluated, and by analyzing the results of compressive strength, it was observed that the highest compressive strength was at the age of 1, 7, 14, and 28 days of the sample with a sand-cement ratio of 4.75 and at the ages of 42, 56 and 90 days, it corresponds to the sample with a sand-to-cement ratio of 4.5 and by analyzing the flexural strength results, it was also observed that the highest flexural strength is related to the sample with a sand-to-cement ratio of 4.5. Then the effect of adding 1% of polymer resin to 11 sand-cement ratio was investigated. From the analysis of the results, it was found that adding 1% of polymer resin at the age of 1 day causes a decrease in compressive strength compared to samples without polymer resin. But with increasing age of samples in high sand-cement ratios, an increase in compressive strength is observed. The highest compressive strength at ages 7, 14, 28, 42, 56 and 90 is for the sand-cement ratio of 4.75 and the highest flexural strength was observed at the sand-cement ratio of 4.5.

Asphalt mortar and asphalt mixture are viscoelastic materials due to the presence of bitumen in their structures. The master curves of dynamic modulus and phase angle developed through the horizontal shifting of the results using the appropriate shift factors are commonly used to describe the viscoelastic properties of asphalt mortar and asphalt mixture. In this study, constructing master curves of dynamic modulus and phase angle of asphalt mortar and asphalt mixture using the least number of test temperatures and frequencies was investigated. The dynamic modulus test was performed on asphalt concrete and asphalt mortar samples at six temperatures and frequencies. Then, the Laboratoire Central des Ponts et Chaussees method was used to determine the shift factors for constructing master curves. Also, the modified Christensen-Anderson-Marasteanu model was fitted on the master curves to predict their viscoelastic properties at an arbitrary temperature and frequency. In addition, the master curves and the fitted models which are created by using test results at two frequencies and six temperatures, six frequencies and three temperatures, or three frequencies and three temperatures, could provide the same predicted values and patterns as the original fitted model with more than 92% accuracy. So, as a result, it is possible to develop the master curves of the viscoelastic properties of asphalt mixture and asphalt mortar with a lower number of test results that have similar accuracy to the original master curves and reduce the time and cost of experiments up to 50%.

Calcium aluminate cement is one of the special cements that performs much better than Portland cement in severe environmental conditions. Engineers, on the other hand, have been critical of this unique cement due to the loss of long-term strength and durability caused by the conversion phenomena. The goal of this study is to improve the durability of calcium aluminate mortar by replacing the cement with pumice powder. In this study, pumice was used as cement substitutes in proportions of 0, 5,15,25, 40, and 60%, and a total of 6 mortar mixes were developed and it was examined in terms of durability properties. The results showed that the plain mixture reached a compressive strength of 33 MPa at the age of 1 day, and 44MPa at the age of 28 days but at 90 days, due to the conversion phenomenon, its strength had decreased by 45%. Pumice had a considerable effect on the strength and, more significantly, the durability properties of mixtures by influencing the conversion phenomena. At the age of 90days, Compressive strength, chloride ion migration coefficient, and electrical resistance, for example, have improved 47%, 78%, and 400% in the ideal mixture (P40) compared to the plain mix. According to the review of the literature, the effect of replacing pumice with CAC cement has not been considered significantly and the effect of pumice on the durability of this type of cement has not been investigated, which can be considered an innovation of this study.

Given the damages to concrete structures caused by different factors, some materials should be used to repair and strengthen them. In general, cement-based mortars are used to repair concrete structures. The shrinkage and inappropriate compaction of repair mortars can reduce the bond strength between mortar and concrete substrate. the shrinkage is an important problem that has an adverse effect on the adhesion between repair mortar and concrete substrate. The shrinkage can create tensile stress inside mortars, leading to cracking due to their low tensile strength. The mortar-substrate interface is of great importance since the improper compaction can create fine pores and lower the bond strength.The suitable compaction of repair mortar while applying it on the concrete substrate is an effective factor in increasing the adhesion between the mortar and concrete. The mortar-substrate interface is of great importance since the improper compaction can create fine pores and lower the bond strength. Therefore, in this study, different prestresses were imposed on repair mortar to evaluate their effects on the shear and tensile bond strength between repair mortar and concrete substrate using friction-transfer and pull-off tests. The role of curing in reducing the shrinkage of mortars was also evaluated. The semi-destructive friction-transfer and pull-off tests were then used to assess the in-situ compressive strength of cement-based mortars. By calculating the correlation coefficient and plotting the calibration curves, relationships were provided to convert the measurements obtained from the semi-destructive tests to the compressive strength of the mortars. Eventually, the cracks and stresses that appeared in the specimens were presented using finite element ABAQUS software. The obtained results indicated the effect of prestress on increasing the shear and tensile bond strength between the concrete substrate and repair layers. Moreover, a high correlation coefficient was found between the measurements of the in-situ and laboratory tests. A good agreement was also observed between the finite element modeling and the experimental results. In some researches, friction transfer and pull-off tests have been used to compare the compressive strength of fiber-reinforced mortars and polymer-modified mortars with the results of the above tests, which has resulted in a very high correlation coefficient between the results.Imposing a prestress of 0.5 kg/cm2 resulted in an increase of 30.1% and 31.4%, respectively, in the shear and tensile bond strength between the repair mortar and the concrete substrate at the age of 90 days. Imposing a prestress of 0.1 kg/cm2 resulted in an increase by 7.5% and 5.8%, respectively, in the shear and tensile bond strength between the repair mortar and the concrete substrate at the age of 90 days. Keeping the specimen in the free space resulted in 64% more shrinkage compared to the one cured in water. The friction-transfer and pull-off test results had a correlation coefficient of more than 0.98 with the repair mortar's compressive strength. Therefore, these tests can be used to evaluate the in-situ compressive strength of mortars. The compressive strength of repair mortar can be calculated by substituting x for the friction-transfer and pull-off test results, respectively, in the equations y=10x-0.805 and y=17.32x+1.83.

Today, the use of different kinds of polymer, as the modifier of some repair mortars properties, is growing. Given the damages to concrete structures, it is necessary to use appropriate repair layers. In concrete structures, concrete and steel are connected, and in most cases, repair layers are applied in direct connections with steel. Therefore, in this research, the shear and tensile bond strength between steel and styrene-butadiene rubber polymer modified mortars was measured using semi-destructive friction-transfer and pull-off tests. In the "pull-off" test, to determine the bond between the mortar and the steel, a core with a 50mm diameter and is first mounted on the test surface using a diamond drill bit and a metal cylinder with a diameter of 50 mm and a thickness of 20 mm is attached to the partial core. Then, the tensile force is applied to the cylinder by means of a "pull-off" device to make the partial core fail. To measure adhesion with friction transfer method, first a small core was created from the mortar surface to the steel substrate surface using the coring machine. Thereafter, the friction transfer metal device was fixed onto the core and the torsional moment was applied using a typical torque wrench in order to cause failure in the core. Moreover, the effect of polymer on the shrinkage of mortar was evaluated. Shrinkage is one of the important problems that negatively affects the adhesion of repair mortar and steel. Due to the fact that hydrated cement paste has capillary pores that contain some water, shrinkage occurs after this moisture leaves the pores. The effect of polymer on mortars was investigated by taking images with a scanning electron microscope and using the “Image-J” and “Origin” software programs. Afterward, in order to evaluate the mechanical properties of mortars, the in-situ compressive and flexural strengths of the mortars were determined, and the calibration curves were plotted by comparing them with standard laboratory tests. Then, relationships were proposed to convert the results of in-situ tests to the compressive and flexural strength of the polymer modified mortars. Eventually, the cracks and stresses that appeared in the mortars were provided using ABAQUS software. The obtained results indicated the effect of polymer in reducing the shrinkage of mortars and increasing the shear and tensile bond strength between steel and mortar, along with a high correlation coefficient between the measurements in the in-situ and laboratory tests. Comparing the modified mortars with polymer and ordinary mortar, it is observed that at the age of 90 days, adding 10, 15 and 20% of SBR reduced the amount of shrinkage to 35.3%, 4.2% and 45.4%, respectively. Addition of styrene butadiene rubber to the repair mortar increased the shear bond strength obtained from the "friction transfer" test between the mortar and steel at the ages of 7, 42 and 90 days by 44.4, 178.2 and 303.1%, respectively. Adding SBR to the repair mortar increased the tensile strength of the "pull-off" test between the mortar and the steel at the ages of 7, 42 and 90 days by 58.7, 183.4 and 291.2%, respectively. A good agreement was also observed between the numerical and experimental results.

In the concrete repair industry, the adhesion between the repair layer and the concrete plays a decisive role in the successful composite performance of the repair layers. Due to the shrinkage and its effect on adhesion loss, in this paper the effect of polypropylene fibers on the adhesion between mortar/concrete has been investigated. A new "twist-off" test has been used to perform the experiments. In all experiments, the results of the "twist-off" test were compared with the results of the "pull-off" test. X-ray diffraction pattern and scanning electron microscopy tests were used to further analyze the results. Also, the effect of fibers on shrinkage and mechanical properties of mortars and its relationship on adhesion between mortar and concrete were investigated. In this regard, the tests of "twist-off" and "pull-off" were used in the laboratory and compared with the outputs of computer modeling. Also, by examining the correlation coefficient between the results of in-situ tests and laboratory tests, calibration diagrams were presented to convert the readings obtained from the "twist-off" and "pull-off" tests into the compressive strength of mortars. The results indicate that for the fibrous sample, the peak intensity of Ca (OH)2 or calcium hydroxide is reduced, resulting in the production of more hydrated calcium silicate or C-S-H gel, which results in improved final properties of the mortar and increased adhesion. Also, on average, the shear and tensile bond strength of 90 days obtained from "twist-off" and "pull-off" tests with the addition of fibers increased by 49.5% and 43.1%, respectively.

Since unreinforced structures have the highest potential for earthquake damage and have multiple failure mechanisms, due to the lack of many uncertainties in the parameters of this type of structures, their vulnerability should be studied with proper knowledge of this and considering the parameters and the most probable modes for its failure. Also, most of the structures that are of historical importance are made of building materials and bricks. These types of structures usually have major weaknesses against earthquakes. Recognition of these weaknesses is a prelude to choosing the appropriate method to strengthen them. In recent decades, researchers have used various methods to enhance the seismic behavior of brick walls. Common methods for this work are coating and reinforcement with plaster and sprayed concrete, which is the most common method of using sprayed concrete. In this study, the micro method is used for finite element modeling in ABAQUS software. In modeling, three methods of reinforcement are used, which include reinforcement with steel sheet, FRP sheet and mortar. The results of this study showed that the sequential arrangement of FRP strips, compared to other methods, had a greater effect on improving the flexibility and the diagonal arrangement of the mentioned strips had a tangible effect on increasing the final strength of masonry walls.

Recent investigations show that graphene oxide nanoparticles (GO) are promising nano-sized additives to enhance the mechanical property of cementitious materials. GO are the product of chemical exfoliation of graphite and contain a range of reactive oxygen functional groups that enable it as a suitable candidate for reaction in cementitious materials through physical functionalization. In this paper, the experimental program is performed to study the mechanical and water transport properties of GO-reinforced cement composites. Experimental results show, adding GO improved the tensile, flexural, and compressive strengths of mortar with the increase in flexural and tensile strength more than that of compressive strength. Especially, the tensile and flexural strength, when the content of GO was 0.05% bwoc, the cement mortar exhibited remarkable increase by 70% and 22% respectively, comparing with those without GO. Particularly, the compressive strength of concrete incorporating 0.1% by weight of cement GO increased by 25% and 50% than those of concrete without GO after curing for 28 days and 90 days respectively. The strengths enhancement can be attributed to the promotion of hydration and the finer pore structure of cement paste incorporating GO. There are thresholds for all mechanical strengths of cement mortar incorporating GO where the GO content exceeds the threshold, the decrease in strength is observed which can be attributed to the deformation of the hydration crystals by the change in the dosage of GO in the matrix. Penetration test results indicate that the incorporation of a very low fraction of GONPs can effectively hinder the ingress of water molecules. It can be concluded that adding GONPs improve the transport properties of concrete which subsequently improves its durability.

Numerical models are feasible approach against field studies which are capable of estimating of materials behavior appropriately if material properties are considered exactly. Numerical models are categorized in three sets: Micro, meso and Macro scale. In macro scale, the whole concrete is considered as a one phase material and usually the interaction between concrete-steel is just modeled. In Micro Scale Modelling, the cement-aggregate crystals are evaluated. The other preference of meso scale numerical model is the ability of presenting different phases interaction in multi phase materials such as concrete. This feature is useful in high rate dynamic load such as explosion. To perform meso scale modeling, different random specimens with different contents of aggregates must be produced. In different studies, a unique pattern which could generate real aggregation is not used. Aggregates generated in this study are elliptical, and by controlling the lack of interference with each other, aggregates are randomly assigned into the defined template boundaries. Then, in the next step, the specimen is meshed by choosing dimensions of elements in cubic form. Finally, the prototype is transformed into the input text file of the numerical analysis programs. The comparison between produced aggregate curve and real cure shows good agreement.

Durability of cement based material due to its uses in the building industry, always has been recognized as one of the main components of sustainable development of infrastructure and urban buildings. One way to improve the durability of concrete, especially in corrosive environments is to use natural pozzolans. On the other hand, with increasing carbon dioxide gas production in cities, the effects of carbonation phenomenon on the durability properties of concrete have increased. In this research, the effect of carbonation phenomenon on the durability properties of mortars containing natural pozzolans is investigated. In sample making two natural pozzolans including Khash pumice and Jajroud trass as substitute for cement by 20% and three water/cement ratios of 0.485, 0.44 and 0.4 were used. In this study, compressive strength test was used as an indicator of mechanical properties as well as an indicator of hydration degree in specimens. In order to study of durability properties of mortars carbonation depth, water absorb capillary and electrical resistance of specimens were measured. According to results, use of natural pozzolans reduces the compressive strength of specimens and increase depth of carbonation in them. Also, electrical resistance increases in samples. The results of capillary absorb water test show that carbonation phenomenon decreases capillary absorption coefficient in some samples. Finally, it can be concluded that the trass samples showed better performance than the pumice at an early age, while the pumice improved with increasing age. It is expected that the pumice performance was better than the pumice with give over time