Pore Size Distribution Of Concrete Research Articles

Comparative study on the static and dynamic mechanical properties and micro-mechanism of carbon fiber and carbon nanofiber reinforced concrete

In order to compare the effects of carbon fiber and carbon nanofiber on the static and dynamic mechanical properties of concrete, the static mechanical tests, dynamic compression test and dynamic splitting tensile test were carried out on carbon fiber reinforced concrete (CFRC) and carbon nanofiber reinforced concrete (CNFRC). Meanwhile, relevant micro-mechanism was analyzed through the MIP test and SEM test. The results showed that both carbon fiber and carbon nanofiber could improve the mechanical properties of concrete and refine the pore size distribution of concrete. In terms of the static mechanical properties, the ductility of CFRC was better, while the strength performance and deformation performance of CNFRC were better. In terms of the dynamic compression mechanical properties, the energy consumption performance of CFRC was better, while the strength performance of CNFRC was better. In terms of the dynamic splitting tensile properties, the strength performance, deformation performance and energy consumption performance of CFRC were better. Under a load, carbon fiber exerted a more obvious “crack resistance effect”, while carbon nanofiber exerted a more obvious “filling effect”. Carbon nanofiber had a better optimization effect on the pore structure of concrete than carbon fiber. The research results could provide reference for the selection of CFRC and CNFRC under different engineering requirements.

Investigation of moisture migration of MWCNTs concrete after different heating-cooling process by LF-NMR

Moisture migration and distribution have a significant influence on the durability of concrete exposed to high temperature after cooling process. And adding multi walled carbon nanotubes (MWCNTs) into concrete could greatly improve its mechanical properties at room temperature. In order to study the moisture content, distribution characteristics and migration law of MWCNTs concrete after different heating-cooling process, a non-destruction method, low field nuclear magnetic resonance (LF-NMR) detection technology was applied in this study. The MWCNTs concrete specimen was heated at 200, 400, 600 and 800℃ followed by two cooling modes, including quenching in pure water and spraying by high pressure water gun. For comparison, plain concrete (without MWCNTs) specimen under the same experimental conditions was prepared as a reference. And then the transverse relaxation time (T2) was measured by Low field nuclear magnetic resonance (LF-NMR) to distinguish the moisture condition of the concrete specimen and the influence of MWCNTs on the moisture migration of concrete after heating-cooling process. Meanwhile, the weighing method also conducted to measure the moisture content to compare with the results obtained from LF-NMR. In addition, mechanical test and micro test (TG-DTA and SEM) were performed to confirm the influence of MWCNTs on the residual properties of concrete. Results from this study showed that the transverse relaxation time T2 of concrete presents a satisfactory correlation with moisture content, residual compressive strength and porosity of concrete after heating-cooling process. And the results of weighing are consistent with those of LF-NMR. Both heating-cooling process affected the moisture migration in concrete, leading to different mechanical performance and pore structure. Furthermore, the MWCNTs have significant effects on moisture migration and pore size distribution of concrete. Based on the LF-NMR test results, the relationships between the residual compressive strength, porosity and moisture content were established.

Review on the Durability of Polypropylene Fibre‐Reinforced Concrete

Polypropylene fibre (PPF) is a kind of polymer material with light weight, high strength, and corrosion resistance. The crack resistance of concrete can be improved by adding PPFs. PPF can optimize the pore size distribution of concrete. As a result, the durability of concrete is significantly enhanced since PPF can block the penetration of water or harmful ions in concrete. This paper summarizes the influence of polypropylene fibre on the durability of concrete, including drying shrinkage, creep, water absorption, permeability resistance, chloride ion penetration resistance, sulfate corrosion resistance, freeze‐thaw cycle resistance, carbonation resistance, and fire resistance. The authors analysed the effects of fibre content, fibre diameter, and fibre hybrid ratio on these durability indexes. The durability property of concrete can be further improved by combining PPFs and steel fibres. The drawbacks of PPF in application in concrete are the imperfect dispersion in concrete and weak bonding with cement matrix. The methods to overcome these drawbacks are to use fibre modified with nanoactive powder or chemical treatment. At last, the authors give the future research prospects of concrete made with PPFs.

Application of Low-Field NMR to the Pore Structure of Concrete

In the present study, we used low-field nuclear magnetic resonance (LF-NMR) measurements and mercury intrusion porosimetry (MIP) to evaluate the influence of the water–binder (w/b) ratio, fly ash (FA) replacement and curing regimes on the pore structure of concrete. The main advantage of LF-NMR is that it is nondestructive and suitable for large concrete samples compared with other traditional methods, such as MIP, adsorption methods and scanning electron microscopy methods. Hence, the LF-NMR relaxometry method measures the pore structures that are closer to reality. The LF-NMR relaxation time, T2, represents the change in the pore structure during the hydration and hardening processes of concrete. The results showed that the T2 spectrum of the concrete sample was mainly composed of 3–5 signal peaks. Additionally, the w/b ratio, FA replacement and the curing regimes have significant effects on the T2 spectrum, porosity, and pore size distribution of concrete. In addition, the compressive strength of concrete has a close relationship with its pore structure. Based on the LF-NMR test results, the relationship between the compressive strength and the porosity, pore size distribution of concrete was established.

Modelling the electrical resistivity of concrete with varied water and chloride contents

The electrical resistivity of concrete is an important property in the assessment of reinforcement corrosion in concrete and an essential parameter in the design and operation of cathodic protection for reinforced-concrete (RC) structures. Water and chloride contents in concrete are highly variable in RC structures in real-world hostile environments, meaning that characterisation of their coupled effects on concrete electrical resistivity is important. The currently available models are investigated in this paper. As all the current models are purely empirical, an improvement with a semi-empirical model is proposed. The improvement highlights the intrinsic linkage between concrete electrical resistivity and water content and the pore size distribution of concrete. The proposed model was tested using two sets of experimental data and was also compared with other two empirical models.

Study on mechanical properties of alkali-resistant basalt fiber reinforced concrete

The alkali resistant basalt fiber (ABF), which are the modified basalt fiber with the property of the alkali resistant, has potential application in concrete. This study investigated the alkali resistance of ABF and the unmodified basalt fiber (BF) by soaking the fibers into the simulated alkaline solution of concrete. The effects of BF and ABF on the mechanical properties of concrete were studied. The results showed that, the compressive strength, flexural strength and splitting tensile strength of the concrete with the addition of 0.1% ABF were increased by 2.5%, 17.2% and 12.1%, respectively. The measurements of mercuryintrusionporosimeter (MIP) and scanning electron microscopy (SEM) indicated that the addition of ABF improved the pore size distribution of concrete. Moreover, the bonding between the fibers and the matrix of concrete was enhanced.

Permeability of Concrete and Correlation with Microstructure Parameters Determined by 1H NMR

Water and gas permeability coefficients of concrete with different water‐binder (w/b) ratios and admixtures were measured by a self‐designed test device based on the steady‐state flow method for liquid and the method of differential pressure in stability for gas, respectively. In addition, the micropore structure of concrete was determined by 1H nuclear magnetic resonance (NMR). Results indicated that there are good correlations between water and gas permeability of concrete with different w/b ratios, with correlation coefficient greater than 0.90. Better correlations between water permeability and segmental contributive porosity ranged from 10 to 100 nm and 100 to 1000 nm can be identified, but the gas permeability is more relevant to the segmental contributive porosity ranging from 100 to 1000 nm. Moreover, the correlation between water permeability and contributive porosity for each pore diameter is always better than that of gas permeability. The influence of admixtures on the relationship between permeability and pore size distribution of concrete is significant. Moreover, water permeability coefficient is one or two orders of magnitude lower than the gas permeability coefficient.

Effect of Metakaolin on the Strength and Pore Size Distribution of Concrete

Metakaolin, a supplementary cementitious material, together or separately with silica fume and fly ash, has been widely used as a replacement material for cement. This research is to determine the effect of metakaolin replacement of cement (0%, 7%, 9% and 12 %) to the 3, 7, 14 and 28-day compressive strengths of wet cured concrete at water/cement ratio of 0.4 and design strength of 40 MPa. The workability of the fresh concrete was measured through slump and compacting factor tests. Results show that the workability of the fresh concrete decreased up to 80% at metakaolin replacement of 12%. Replacing metakaolin by 12 %, on the other hand, had resulted in the highest compressive strength, which is 48.5 MPa at 28 days compared to control and other percentages of replacement. The porosity measured on the broken samples taken from the compressive strength test shows that the pore diameter size of metakaolin concrete is almost 93% finer than the controlled concrete, which had contributed to the increased in the strength. The use of metakaolin as supplementary cementitiuos material is hoped to be able to replace or stand tall as others similar to it in the market either due to its strength or cost.

Effect of Metakaolin-Based Modifier on the Permeability of Concrete Structure in the Marine Environment

Corrosion of the steel reinforcement in the concrete structure caused by chloride ion penetration becomes more serious in the marine environment. Metakaolin has been widely used in the concrete structure to improve the strength and durability. The combination of metakaolin (MK) and fine fly ash (FA) was studied in the article and the penetration behavior of concrete with various contents of metakaolin-based modifier is investigated. The penetration resistance of concrete was tested in combination of electric flux test. The improving mechanism was studied with mercury intrusion porosimetry analysis (MIP). The experiment results indicate that metakaolin-based modifier improved the penetration resistance of concrete obviously. The combination of fine fly ash weakened the water sucking action of metakaolin and preserved the working performance of concrete. The pore size distribution of concrete containing metakaolin-based modifier has been optimized to improve the microstructure and enhance the penetration resistance of concrete.

Experimental Analysis of Relationship between Pore-Structure and Frost-Resistance of Concrete

The influence of admixture on concrete pore structure was analyzed by using the mercury intrusion method and the rapid frozen-thaw method under the condition of the same water/binder ratio in this paper, and thus the relationship between pore structure and frost resistance of concrete were analyzed. When the compound mineral ad-mixture is mixed, the porosity rate of concrete can be decreased and the harmful hole is in-creased, the less-harm hole and the no-harmful hole are decreased. The early strength of concrete is not decreased. But the strength has the increasing trend in the late, which is more favorable for the impermeability and corrosion resistance. But the improvement of the freezing resistance is not obvious. The admixture of air entraining agent can increase the porosity and more-harmful hole, and the concrete strength will be decreased, which will be not favorable for the freezing resistance of concrete. If these two substances are admixed at the same time, the concrete porosity is increased, and the pore size distribution of concrete can be reasonable. The decrement of concrete strength is not obvious, but it is favorable for the freezing resistance of concrete.

Influence of recycled aggregates on long term mechanical properties and pore size distribution of concrete

Abstract This paper presents the results of a study of the long term mechanical properties and pore structures of recycled aggregate concrete. In this study, two different sources of recycled aggregates were used to replace natural aggregate at a level of 100%. The compressive and splitting tensile strength of the concrete were tested, and the pore structures of the concrete were analyzed. The results showed that after 5 years of curing, the recycled aggregate concretes had lower compressive strength and higher splitting tensile strength than the corresponding natural aggregate concrete. However, from 28 days to 5 years, the increase of compressive and splitting tensile strengths was more in the recycled aggregate concretes. After 5 years of curing, the concrete made with 100% of crushed old concrete aggregate had the lowest porosity. Good correlations were found between compressive and tensile strength and porosity.

Prediction of the hydraulic diffusivity from pore size distribution of concrete

A model is presented in this work through which variation of hydraulic diffusivity of concrete with relative water content can be obtained from pore size distribution as an input. The specific water capacity and hydraulic conductivity of concrete are expressed in terms of pore size characteristics, considering laminar flow due to capillary suction through tortuous elliptic tubes, oriented equally in three orthogonal directions. Hydraulic diffusivity being the ratio of hydraulic conductivity and specific water capacity is thus expressed in terms of pore size characteristics. The input pore size distributions have been determined experimentally for normal strength concrete mixes through mercury intrusion porosimetry. Using the model the variation of hydraulic diffusivity with relative water content is determined for three cases viz. 1) ideal continuous wetting, 2) ideal continuous drying and 3) random access of pores by water. These results are then compared with an experimentally obtained variation.

Change of pore size in concrete due to electrochemical chloride extraction and possible implications for the migration of ions

Electrochemical chloride extraction (ECE) is used for the rehabilitation of chloride-contaminated concrete. Anions such as chloride and hydroxide are pushed away from the cathode (reinforcement), and cations such as sodium, potassium and calcium are attracted to the cathode. During ECE an increase of the concrete resistance can be observed. The results of a petrography study on ECE-treated concrete are presented in this paper. It also investigates the influence of pore size on ion migration using a concrete substitute model with known pore size. Findings showed that the pore size and pore size distribution of concrete are altered due to ECE. It is therefore suggested that concrete acts as active migration medium in the migration process by releasing ions into the pore solution. Moreover, small pores hinder the migration of ions, which may partially be responsible for changes in concrete resistance.

Study on some factors affecting the results in the use of MIP method in concrete research

Effects of rate of pressure application and forms and type of sample on porosity and pore size distribution of concrete estimated through mercury intrusion porosimetry (MIP) are presented in this experimental work. Two different forms of concrete sample, namely, crushed chunks of concrete and small core drilled out from the concrete beam specimens, were used for this study. The results exhibit that the rate of pressure application in mercury porosimetry has little effect on porosity and pore size distribution of concrete. It is also demonstrated that small cores drilled out from large concrete specimens are preferable as samples for performing porosimetry test on concrete.

Trial of Parsey's compressed air locomotive

Effects of rate of pressure application and forms and type of sample on porosity and pore size distribution of concrete estimated through mercury intrusion porosimetry (MIP) are presented in this experimental work. Two different forms of concrete sample, namely, crushed chunks of concrete and small core drilled out from the concrete beam specimens, were used for this study. The results exhibit that the rate of pressure application in mercury porosimetry has little effect on porosity and pore size distribution of concrete. It is also demonstrated that small cores drilled out from large concrete specimens are preferable as samples for performing porosimetry test on concrete.