جستجوی مقالات مرتبط با کلیدواژه « پومیس » در نشریات گروه « عمران »

Considering the successful usage of alkali activated mortars in several countries and limited research on the durability of these materials, in this paper, permeability and durability of alkali activated slag and pumice mortar in chloride environments have been studied. In order to investigate the mechanical properties and permeability of alkali activated slag and pumice mortars tests such as workability, compressive strength, capillary water absorption, water absorption, chloride ion penetration in the Persian Gulf environment and mercury intrusion porosimetry have been conducted.The results show that the compressive strength of alkali activated slag mortar containing potassium hydroxide was slightly higher than the compressive strength of samples containing sodium hydroxide. In addition, the use of 10% pumice instead of slag has increased the compressive strength of alkali activated slag mortar. Also, the 91-day compressive strength of alkali activated mortars cured in the water was 48.4% higher than those cured in the air. In general, the diffusion coefficient of chloride ions in alkali activated slag mortars was lower than the diffusion coefficient of chloride ions in Portland cement mortar, which was due to less porosity in alkali activated slag mortars and the denser structure. Also, alkali activated mortars containing 90% of slag and 10% of pumice had the lowest diffusion coefficient of chloride ions and Portland cement mortar showed the highest one, which was well matched with the result of capillary water absorption coefficient.

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.

Previous researches have shown that due to its good adhesion, alkali-activated materials can be used as a protective overlay for concrete structures. However, the mechanical properties and durability of alkali-activated materials are not fully investigated. In this paper, compressive strength, bond strength, water penetration and half-cell corrosion potential of alkali-activated slag and pumice mortars as concrete overlay are investigated. The results show that the performance of alkali-activated slag mortar is better than Portland cement one in above tests and the use of potassium hydroxide as activator and a mixture of 90% slag and 10% pumice as based material result in the highest compressive strength and bond strength and the lowest water permeability and half-cell corrosion potential. The initial half-cell potential reading of alkali-activated mortar specimens was an average of 1.9 times more than Portland cement mortar specimens. This difference indicates that the ranges presented in ASTM C876 and their relationship with rebar corrosion risks are not applicable for alkali-activated materials and it is necessary to provide other criteria for these materials. Also, due to different conductivity of alkali-activated and Portland cement mortars, applying potential difference to accelerate the penetration of chloride ions and comparing the performance of alkali-activated materials with Portland cement is not a correct method. However, this method is suitable for comparing mixes design of alkali-activated mortars and the its results are in accordance with non-accelerated methods.

Nowadays, explosion phenomenon has been considered by structural engineers due to the increase of terrorist attacks and unforeseen events. Therefore, the calculation of the final dynamic loads resulting from these loadings should be considered as a criterion in order to design structures and protect military buildings. In this investigation, the behavior of pumice hybrid-fiber reinforced concrete slabs under blast loading was assessed. To evaluate the performance of pumice hybrid-fiber reinforced concrete, contact explosion test on slabs with dimensions 100×100×10 cm was conducted. Six slabs including one unreinforced concrete slab and five fiber reinforced concrete slabs were prepared. Also, C4 explosive material was used to investigate different failure modes of slabs. The results showed that the addition of various types of fibers improved the behavior of slabs. The results showed that the addition of various types of fibers improved the behavior of slabs .Also, it is concluded that replacement of cement and steel fibers with pumice and polyolefin fibers, respectively, led to a slight increment in number and extent of cracks, however, the costs were significantly decreased.

Using fibers to reduce cracks and increase the joint spacing of concrete slabs has become popular in the concrete pavements of airports and freeways recently. However, their durability behavior against acid rain has been less studied. The purpose of this paper is to investigate the mechanical performance and durability of concrete reinforced with polyolefin and polypropylene fibers containing 15% of pozzolanic materials (pumice or metakaolin) instead of Portland type II cement. In this regard, compressive and flexural strength were measured to investigate the mechanical behavior of the studied mixtures at different ages. On the other hand, chemical resistance against acid rain simulated was investigated through the visual examination and weight loss, and also microstructural analysis was performed by SEM analysis and CT scan testing. Based on these results, the addition of both of these fibers in concrete reduces the compressive strength of concretes compared to the similar content in the control concrete. On the contrary, fibers increased the flexural strength, which became much more significant with the addition of pozzolanic materials. However, ordinary and fibrous concrete containing pozzolanic materials showed a weak performance against acid rain. Based on the results of CT scan and SEM analysis, concretes containing pozzolanic materials have a porous structure. Besides, the ratio of calcium to silicon in them is much lower than the control concrete due to decalcification reactions caused by acid attacks.

In the past, fiber reinforced concretes (FRC) was used mainly in pavements and industrial floors however, FRC has a number of other uses as well, with recent uses including bridges, hydraulic structures, tunnels, pipes, canal linings and safety vaults. On the other hand, the resistance of FRC against to penetration of chloride ions, especially bonded chloride, has received less attention. In addition, the prior literature's results on chloride ions bound in different concretes have always been varied. This study analyses the mechanical characteristics of fibrous and normal concretes (NC) containing two pozzolans of metakaolin and pumice using microstructural investigation. Also, the chloride isothermal under marine environment was studied by simulating the immersion and tidal conditions. This study can be beneficial for use in different applications such as paving and bridges which are under the influence of chloride ion penetration. The first goal of this study is to increase the flexural strength of the pavement layer in order to reduce its thickness which can be economical, and the second goal is to study the durability performance of NC and FRC containing of cementitious material (pumice and metakaolin) with respect to the aggressive medium that is a determining factor in the lifetime of concrete structures. It is generally acknowledged that blocking the paths of chloride penetration by densifying the microstructures of the concrete can be a fundamental solution using pozzolanic reaction produced by pozzolans to enhance the durability of concrete. In the last years, metakaolin and pumice has been introduced as a highly active and effective pozzolan for the partial replacement of cement in concrete. Metakaolin and pumice consumes the Ca(OH)2 that is produced from the cement hydration process rapidly and effectively and in addition to CSH, phases like C2ASH8 (stratlingite), C4AH13 and C3ASH6 (hydrogarnet) are produced. These pozzolanic products enhance the structural properties of concrete and also contribute to total pore refinement. In this study, six concrete mixtures with a control mixture without any addition are prepared and tested in hardened states. Afterwards, the resistance to chloride penetration both in immersion and tidal conditions is investigated. Accordingly, first, the compressive strength and flexural strength test were performed on hardened states to assess the mechanical resistance of the different prepared mixtures at early ages and up to 365 days. Then, the microstructure study of six prepared mixtures were investigated by using Scanning Electron Microscope (SEM), EDX spectrum and CT scan test. Finally, the chloride penetration resistance of the different concrete mixtures was evaluated by measuring water-soluble chloride profile, bonding and total chloride in immersion and tidal conditions. In both the immersion and the tidal conditions, durability results show that metakaolin and pumice have a significant effect on the increasing chloride penetration resistance. This impact was far more apparent in pumice-containing samples. However, the concretes containing pozzolans have a porous structure, according to computed tomography scan (CT scan) analysis and microstructure results in this study, and the Ca / Si ratio is considerably lowered owing to decalcification. Also, the results showed that despite the structural porosity in concretes containing pozzolans, factors such as Ca / Si ratio and pore solution concentration play a very important role in their durability against chloride ion in the simulated marine environment.

In this study, 19 different mixtures, including 11 air-entrained mixtures, three flowable mortar mixtures, and five self-consolidating concrete mixtures were fabricated to investigate the effect of different factors, including air content, type and composition of pozzolans, and water to binder ratio(w/b) on electrical resistivity. These mixtures were made by substituting between 30-60% of cement weight by pozzolanic materials with 0.28 to 0.34 w/b ratios. The pozzolanic materials included zeolite, pumice, wollastonite, and slag. Electrical Surface and bulk resistivity tests were performed at different ages on 100 mm x 200 mm cylindrical specimens, and the relationship between the test results was investigated. The results of the study indicated that the electrical resistivity is related to the water to binder ratio, type and composition of pozzolans used, replacement level of pozzolanic materials, and entrained air amount. Among these factors, the w/b ratio and the replacement level of pozzolan used had a greater effect on the electrical resistivity of concrete. The combination of slag and zeolite had the greatest effect, and the combination of slag and wollastonite had the least effect on the development of electrical resistivity results in the mixtures. The result of regression analysis showed that there is a strong correlation between the results of bulk and surface resistivity of concrete at different ages.

Calcium aluminate cement (CAC) is considered as a specific cement due to its special properties and maybe have improved performances compared to the Portland cement under some severe conditions. Although alumina cement has many advantages, it is not widely used in the construction industry because it obtains reduced strength in the long term and has not been adequately investigated. In this study, an attempt is made to improve the durability and mechanical properties of mortars with this type of cement using supplementary cementitious materials (SCMs) such as pumice, zeolite and limestone powder in high cement replacement levels. In this study, porosity, rapid chloride migration and acid resistance tests were employed to investigate the durability properties. In addition, the microstructure of the mixtures was investigated using scanning electron microscopy (SEM). The SCMs were used as cement substitution in proportions of 25, 40, and 60 % and a total of 10 mortar mixes were investigated. The results indicated that the pumice and zeolite significantly improved the mechanical strength and durability properties of the mixes. The microstructural studies revealed one of the most important reasons for the reduction of the compressive strength of the plain mixture. The results of this study show that the use of pumice and zeolite mitigates the conversion process, resulting in better performance of the mixes compared to the plain mixture.

Porous concrete refers to a combination of cement and water, without fine grains or with a small amount of fine grains, which is important in terms of water transferability and permeability. This material can act as a drainage and carry rainwater and enhance groundwater. In the present article, the effect of replacement of pumice mineral additive with aggregate of porous concrete with volumetric percentages of 25, 50, 75 and 100% was studied on compressive strength, permeability coefficient and porosity percentage. Laboratory analysis was performed using SAS 9.4 software at 95% confidence level for all samples. The results show that with the replacement of the pumice additive in the structure of the porous concrete and the corresponding removal of the aggregate, the compressive strength of the samples is reduced due to the porosity of the pumice structure and the permeability coefficient and porosity increase. The reduction of compressive strength with increasing pumice percentage for all samples was 60.49, 83.86, 85.96 and 86.98%, respectively. Increasing the permeability coefficient with increasing pumice percentage for all samples was 10.13, 14.96, 18.7 and 24.94%, respectively.

From a strength point of view, lightweight concretes are categorized into three groups of structural, semistructural and non-structural concretes. The main purpose of this research is to determine the optimum mix design of a semi-structural lightweight concrete composed of pumice aggregates with the lowest unit weight and a reasonable compressive strength. For this purpose, the Taguchi method, with four eective factors and three levels, has been adopted. The method is a systematic design of experiments which can eciently reduce the time and cost of experiments. In this method, the most eective factors are selected and dierent levels are determined for each factor. Then, based on the number of factors and the assigned levels, a suitable orthogonal array is chosen using the Taguchi guideline. These arrays can provide a regular program for the experiments, including the number of tests and the combination of dierent levels in each test. At the end of each test, the corresponding quality criterion is obtained. Using the results of systematic tests via MINITAB software, the optimum combination is determined and, thus, the value of the quality criterion under optimum condition is predicted. In order to validate the accomplished study and evaluate the Taguchi method, a proof test, based on the optimum combination, is usually built, and its result is compared with the software prediction. In this research, due to the numerous factors aecting the compressive strength and unit weight of concrete, four governing factors are selected: pumice with sieve type 1, pumice with sieve type 2, sand and ller. In addition, pumice with sieve type 3 has been also selected as a complementary factor. The remaining materials, such as the ratio of water to cement, additives and cement weights, are considered as constant. In order to determine the optimum combination, the orthogonal array of L9 is utilized and after the analysis and determination of optimum levels, the results of laboratory proof tests and prediction of the Taguchi method were compared. The results demonstrate that the systematic Taguchi design method is very useful in reaching the optimum mix design of semi-structural lightweight concretes.

In the last decade, porous (pervious) concrete has been used in sidewalks and surface pavements for collection of urban runoff water. Porous concrete is highly considered for its hydrailuc conductivity and water transport capacity. In the present research, the original porous concrete was made of 1400 kg/m3 aggregates and 330 kg/m3 Portland cement, along with water to cement ratio (W/C) of 0.35-0.45. In the mixture of porous concrete and additive, the following additives were used: zeolite, perlite, pumice and clay aggregate, with type 2 and type 5 Portland cement. Compressive strength and permeability coefficient (hydraulic conductivity) were studied. Results revealed that adding additives decreases compressive strength of the porous concrete. This reduction in compressive strength for the highest and least amount of zeolite, perlite, pumice and clay aggregate was 13, 48.4, 10.1 and 12.6 percent, respectively. Hydraulic conductivity increased in most of the treatments, except perlite. The highest increase in hudraulic condictivity (7.3 %) occurred in the treatment containing 5% pumice and the highest reduction in hydraulic conductivity (3.7 %) occurred in the treatment containing 10% perlite. In general, among the different additives used in this experiment, the treatment containing 10% perlite had the highest compression strength (11.95 MPa) and the treatment containing 10% clay aggregate had the lowest compression strength (3.2 MPa). This shows that adding clay aggregate reduces compression strength of porous concrete more than other additives. The perlite additive ranks next.

This paper discussed the effect of adding a pumice pozzolans and metakaolin composition on durability properties of self-compacting concrete (SCC) to present a corrosion-resistant mixed to be used for decks and piers of bridges in sea areas, and marine structures. Replacement of 10% pumice and 10% metakaolin and their 10% and 15% compositions as the replacement of some part of cement were used for making mix plans of the research. Compressive strength, water permeability, specific electrical resistivity, rapid chloride migration tests (RCMT), and accelerated corrosion tests were carried out. The tests were performed at the ages of 7, 14, 28, 56, 90, and 180 days. The results showed that a pumice and metakaolin composition maintained SCC’s mechanical properties, improved concrete durability, and increased age cracking in the accelerated tests considerably as compared with a control sample. The samples reduced RCMT up to 28.1% and increased age cracking by 26.4%.

In this study the possibility of improving the properties of binary concrete containing pumice is investigated, by combined use with silica fumes and development of high performance mixes suitable for the harsh environment of the Persian Gulf. Ternary mixes based on the combined use of 15% and 30% pumice and 2.5%, 5% and 7.5% silica were considered. Concrete mixes were evaluated using compressive strength tests, electrical resistance tests, the rapid chloride permeability test (RCPT) and the rapid chloride migration test (RCMT) at various ages up to 180 days.The results show that simultaneous use of silica fumes and pumice overcomes the deficiency of the slow rate of strength gain that binary mixes containing pumice usually exhibit. In addition, the use of ternary mixes results in considerable improvement in durability at all ages when compared with the control and binary mixes. By using appropriate combinations of pumice and silica fumes it is possible to achieve good strength and durability characteristics at 28 days, along with excellent long term durability.

Self-consolidating concrete (SCC) has been used increasingly over the last two decades, especially in the pre-cast concrete industry because of its ability to consolidate without vibration even in congested areas. The development of SCC mixture design has been driven mostly by private companies who desired to utilize advantages of SCC. Consequently, there exists limited public information regarding the performance of SCC mixtures. In addition, SCC can be characterized as flowing concrete without segregation and bleeding, capable of filling spaces and dense reinforcement. Further it should be able to flow through, and completely fill the form without vibration. Due to the technical and economic advantages that can be accrued by the use of pozzolans, they play an important role when added to Portland cement by usually increasing the mechanical strength and durability of concrete structures.This paper present, an experimental study on the properties of different self-consolidating concrete mixes containing three types of pozzolanic materials in comparison with SCC mixtures without any pozzolanic materials and conventionally vibrated concrete mixtures. Silica fume, pumice powder and rice husk ash were used for both cement and filler replacements. Various experiments such as slump-flow, J-ring, L-box, V-funnel and sieve segregation resistance were investigated for fresh concrete. Further, compressive strength,water and chloride-ion permeability and capillary water absorption at various days were carried out to determine the properties of self-consolidating concretes. The test results indicated that pozzolanic materials such as RHA and VP can be used to produce SCCs. Regarding the strength properties, the test results showed that the 270-day compressive strength of ordinary SCC is about 70 MPa, while SCC mixtures containing SF, RHA and VP have strengths more than 90, 77 and 76 MPa, respectively. In addition, the results proved that artificial and natural pozzolans enhanced the durability of SCC and reduced the penetration, significantly. For instance, adding 15% pumice and 7% silica fume in the SCC specimen reduced the water depth at 90 days by 19% and 54%, respectively.

In this study, the stress-strain behavior of lightweight aggregates concrete (LWAC) made of local Scoria and Pumice aggregates in Azarbaijan-Iran has been studied. Fourteen different concrete mixes with different mix proportions were used in this work. Forty-two cylindrical specimens made of different concrete mixes were prepared for uniaxial compression test to determine the stress-strain behavior of the LWAC. The trend of the experimental results were compared with the existent mathematical relationship defined by other researchers. There were some differences between the experimental results and existing equations which can be related to different properties of the LWAC in comparison with those of normal and high strength concrete (HSC). The experimental results can result in lower flexural strength of the beams than that of the existing relation by other researcher, which implies more attention to be paid on it.

As the use of Self Compacting Concrete becomes common, the risk of exposing it to elevated temperatures increases. However, few investigations have been reported on the mechanical properties of SCC when it is exposed to elevated temperatures.Mechanical properties of SCC containing Pumice (P) at elevated temperatures up to 800°C were experimentally investigated in this paper. Four different mix designs, Traditional Concrete (TC), SCC and two other SCC mixtures containing pumice as a replacement for both cement and filler were produced. At the age of 28 days, the specimens were placed in an electrical furnace and heating was applied at the rate of 2.5 (°C/min) up to the desired temperature. Maximum temperatures of 200, 450, 600 and 800°C were maintained for 2 hr. Then, the specimens were allowed to be cooled in the furnace and subsequently tested for compressive strength, rebound hammer, ultrasonic pulse velocity and weight loss. The residual compressive strength of SCC mixture containing pumice as a filler replacement almost was higher than the other mixtures up to 800°C.

In this research, the properties of structural lightweight aggregate concrete (LWAC) made of local lightweight aggregates in East Azarbaijan-Iran were investigated. Considering Iran earthquake zone, the weight of structures is of high importance. Reducing the weight of building using lightweight aggregates is one of the methods to decrease the harmful effects of earthquake on structures. In this study two different types of lightweight aggregates, Scoria and Pumice, provided from Azarbaijan-Iran, were used in concrete mixes. Mechanical properties of LWAC, including compressive strength, tensile strength, modulus of rupture, modulus of elasticity and stress-strain relationship were studied. In spite of NWC, the results show that at the same conditions, strength of aggregates is the main factor controlling the compressive strength of LWAC. Twenty-seven different concrete mixes with different 28 days compressive strengths varying from 24 to 51 Mpa were used in this study to measure the compressive strength, tensile strength, modulus of rupture, modulus of elasticity and strain at maximum stress which were compared with those of NWC. It was found that for the same compressive strength (24-51 Mpa) the modulus of elasticity of LWAC (10.92-18.77 Gpa) was less than that of NWC (17.53-28.31 Gpa) and tensile strength and modulus of rupture of LWAC was also less than NWC. The corresponding strain of the maximum stress in LWAC was found to be in the range of 2.55-3.78 mm/m, whereas for the same compressive strength, it was at range of 2.28-3.41 mm/m in NWC, this imply to lower modules of elasticity in LWAC compared with NWC.

Stress distribution in lightweight aggregates concrete (LWAC) has been investigated in this research. Many studies have been already done on structural behavior of LWAC، however its properties are not well known as those of NWC. There are many provisions in different codes as equations or recommendations for designing reinforced concrete structures which are applicable for NWC. Because of different roles of aggregates in LWAC and NWC structural behavior of the LWAC needs more investigation. One of the characteristics which are applied as designing parameters is characteristic curve (stress-strain) of the concrete. In this research the stress-strain curve of the LWAC made with Scoria and Pumice has been studied. A total of 27 concrete mixes of LWAC made of scoria and pumice were tested and their stress – strain relationships have been studied. The experimental results show that rectangular stress block required to designing of LWAC structures are need more attention. The estimated flexural capacity with existing equations in codes comparison with experimental flexural capacity in LWAC is greater which lean lead to unsafety in structures. In this study، new equations for stress- strain behavior of LWAC are presented which can lead to prediction of more safe and accurate ultimate flexural strength.