Transport Properties Of Concrete Research Articles

Engineering and gamma-ray attenuation properties of steel furnace slag heavyweight concrete with nano calcium carbonate and silica

As the nuclear energy sector continues to grow worldwide, the improvement of concrete’s radioactive isolation properties for preserving both the environment and human lives in nuclear power plant applications has received a global interest among researchers. Although nano-silica, nano-calcium carbonate, and steel furnace slag have high molar mass and favorable physical properties to improve the concrete’s radioactive insulation properties, scarce literature on the subject matter has been published. The goal of this study is to investigate the appropriateness of using nanomaterials such as nano-silica slurry and nano-calcium carbonate as additives for the production of steel furnace slag (aggregate of steel furnace slag: ASFS)-based heavyweight concrete (HWC) with improved durability, mechanical strength, and gamma (γ)-ray attenuation properties. A new contribution of the study is the use of nano-SiO2 slurry and nano-CaCO3 in concrete binder formulation to enhance concrete gamma-ray shielding capability. An optimized content was developed for the nano calcium carbonate, in combination with a constant amount of nano-silica slurry, to improve the performance of the HWC. An investigation program was implemented with eight concrete mixes, which were prepared by utilizing ASFS as the main aggregate with 3% of nano-silica slurry in combination with (0–3%) of nano-calcium carbonate as additives to produce high strength HWC. The hardened concrete samples were evaluated for mechanical strength, fluid transport and γ-ray shielding properties. The effect of 3% nano-SiO2 slurry and 2.0% nano-CaCO3 on the compressive strength and gamma-ray shielding increased by 10.3 and 3.4%, respectively, at 28 days as compared to the control mix without nanomaterials additives. The other mechanical and fluid transport properties of the concrete were also improved significantly. In conclusion, the combined use of nano-silica slurry and nano-calcium carbonate would enhance the mechanical strength, fluid transport and γ-ray shielding properties of steel furnace-slag heavyweight concrete.

Assessing the Performance and Transport Properties of Concrete using Electrical Property Measurements

Assessing the Performance and Transport Properties of Concrete using Electrical Property Measurements

Chloride penetration in shrinkage-compensating cement concretes

Shrinkage-compensating cement (a.k.a., Type K expansive agent) is a calcium sulfoaluminate cement with the ability of providing volume expansion during early age, primarily due to the formation of ettringite. Despite the past studies on the strength, shrinkage, and hydration of shrinkage-compensating cement concretes, there was no systematic investigation to understand the performance of this type of concrete under exposure to aggressive agents, particularly chloride ions. To address this gap, a holistic testing program was established in this study to evaluate the strength, dimensional stability, and transport properties of concretes made with various dosages of Type K expansive agent. This included compressive strength, drying shrinkage, rapid chloride penetration, electrical resistivity, rapid chloride migration, and absorption tests. Both helium and mercury intrusion porosimetry analyses were also performed to further explain the experimental test results with the findings related to the distribution of pores. The results of this study confirmed the benefits of using Type K expansive agent (up to a certain dosage) in terms of increased compressive strength and reduced drying shrinkage. However, it was revealed that the permeability of concretes made with this type of cement is adversely affected. This issue was addressed by the identification of optimal dosages of supplementary cementitious materials, including fly ash and silica fume. Upon completing the necessary experiments on the improved mixtures, this study reported how low-shrinkage concretes with low susceptibility to chloride penetration can be developed with the promise of application in a wide variety of civil infrastructures exposed to harsh environmental conditions.

Microstructure Model for Predicting the Sorptivity of Concrete Mixtures

Durability of concrete structures is determined by the mass transport properties of concrete. The performance of concrete exposed to aggressive environments is a function mainly of the penetrability of the pore structure i.e. the rate of absorption (sorptivity) due to capillary rise. This study involves the development of a predictive sorptivity microstructure model accounting for the type of cement, cement degree of hydration, mixtures proportion, aggregates gradation and packing density, and air content. This paper presents the formulation and validation of a sorptivity model. An experimental program is designed to evaluate the proposed model. Evaluation of the proposed model revealed that the model is a good fit to the experimental data and does not contain outliers or discerning pattern. The corresponding standard error and correlation coefficient are 0.00039 mm/s1/2 and 0.89, respectively. Results of statistical evaluation revealed that the proposed model is significant in its prediction of the outcome, where the p-value was found to be less than 0.001. The proposed predictive sorptivity model can be employed in the design of concrete mixtures to meet specific durability requirements as a priority and ensure quality control. Furthermore, the proposed model can be utilized to improve the durability prediction of concrete mixtures.

The tin can method for determining moisture transport properties of concrete

Traditional methods for measuring moisture transport properties of concrete are time-consuming, especially since thick specimens are required, and steady-state methods are preferred. Non-steady state methods may be an alternative but the conditioning to uniform initial conditions is extremely difficult. The tin can method is, however, a good alternative under certain conditions and for certain concretes. Concrete is poured into a tin can and sealed cured in this way for at least a month. The can is opened, and the concrete is dried in a constant climate. Weight changes are recorded for several weeks. From these weight changes, the initial RH at start of drying, the drying climate and the desorption isotherm, the moisture transport coefficient or the moisture diffusion resistance factor are derived. The paper describes the theory behind the method and the unique conditions available for certain concretes that makes the method applicable. Examples of measurements are shown for a number of concretes and verification is done with the cup method on the very same concretes, with excellent results.

Effect of high-volume ultrafine palm oil fuel ash on the engineering and transport properties of concrete

Palm oil fuel ash (POFA) is a by-product in palm oil manufacturing and is currently disposed to open areas and landfills without any previous treatment, thereby causing environment pollution. The use of small-particle-sized ground POFA to prepare ultrafine POFA (UPOFA) is a suitable method to improve its characteristics as a supplementary cementitious material. Although high-volume POFA exhibits reduced mechanical properties in the early ages, heat treatment and further grinding reduce its carbon content and increase its pozzolanic activity. In this study, UPOFA was used to minimise the cement content in concrete mix. Cement was replaced with UPOFA at 0 %, 20 %, 40 %, 60 % and 80 % ratios to produce green concrete. Results revealed that the UPOFA showed remarkable improvement in concrete strength, especially with 20 % and 40 % substitution levels. By contrast, the compressive strength reduced at high replacement levels to be 34.5 MPa at 28 days. The water absorption of concrete containing UPOFA is considerably reduced, thus improving the concrete’s durability.

Development of water-resisting mortar by incorporation of functionalized waste incineration ashes

In this study, a method to prepare water-resisting mortars by incorporating hydrophobic incineration ashes is reported. Bottom ash is the by-products of municipal solid waste incineration with limited recycling options due to harmful contaminants. To decrease the environmental risk of bottom ash and provide an economical and green route to reuse it, a wet chemistry method is applied to prepare hydrophobic bottom ash and investigate its potential to improve transport properties of concrete. The functionalization of fine bottom ash (<0.125 μm) using stearic acid provides hydrophobic nature to the particles along with improved leaching properties. At an optimum addition of 4% stearic acid, the bottom ash present a water contact angle of 141° and can be classified as hydrophobic. The influence of functionalized bottom ash on the cement hydration, mechanical properties, water absorption and wetting property of the water resisting mortar is investigated. Results show that the up to 30% of the binder can be replaced by hydrophobic bottom ash as it decreases the capillary water absorption rate and chloride penetration depth by 57% and 65%, respectively. The samples containing hydrophobic bottom ash show better mechanical properties as compared to the samples made with untreated bottom ash. The environmental assessment shows that the mortars containing functionalized BA are environmentally friendly because of the dilution effect and immobilization potential of the hazardous material into the cementitious matrix. Results show that the proposed method is a facile and efficient way to change bottom ash into hydrophobic powders, which leads to more environmentally friendly water-resisting mortar.

Use of metakaolin as supplementary cementitious material in concrete, with focus on durability properties

Numerous research efforts on metakaolin as a supplementary cementitious material (SCM) have been undertaken in the past 20 years. This material, while relatively expensive mainly due to low production volumes worldwide, nevertheless has a significantly lower production cost than Portland cement. However, industry remains tentative in considering metakaolin in concrete. This paper takes the view that industry should consider investing in the production and application of metakaolin in appropriate concrete projects, particularly in aggressive environments where plain Portland cement may be inadequate, and where other SCMs may not readily be available. The main contribution of the paper is a global review of recent studies on the use of metakaolin in different types of concrete. This international experience is then compared with results from a study on the durability performance of metakaolin concrete using local materials in the Western Cape province of South Africa, as a means of concrete performance improvement. The study investigates concrete durability properties: penetrability (sorptivity, permeability, conductivity and diffusion), mitigation of Alkali-Silica Reaction (ASR), and carbonation resistance. The concretes were prepared with three water-binder ratios (0.4, 0.5 and 0.6), and with metakaolin replacement levels of 0% (control), 10%, 15% and 20%. Performance results show that, with increasing metakaolin content, the transport properties of concrete are considerably improved, ASR expansion due to a highly reactive local aggregate decreases to non-deleterious levels, while no detrimental effect on carbonation is observed. Thus, metakaolin could serve as a valuable SCM to enhance the durability performance of concrete in local aggressive environments.

Capillary Absorption and Oxygen Permeability of Concrete Reinforced with Carbon Nanotubes

Abstract This article focuses on the transport properties of concretes reinforced with different amounts (0.05–0.5 wt.%) of pristine and functionalized carbon nanotubes (CNTs) with distinct aspect ratios (300, 667). To this end, concretes with different water-to-cement ratios were tested at distinct ages in terms of capillary absorption and oxygen permeability. The results show the ability of CNTs to decrease both capillary water absorption and oxygen permeability up to 42 and 71 %, respectively, depending on the type and amount of CNTs. Compressive strength increased up to 21 %. The best performance was found for 0.1 % CNTs of a lower aspect ratio. Higher amounts of CNTs did not lead to a proportional reduction of transport properties. CNTs were more effective in dried concrete compared to saturated ones where they could better participate in the pore refinement and microcrack retention. Transport properties correlated well with compressive strength, but oxygen permeability was greater affected by the incorporation of CNTs than other tested properties.

Transport Properties of Concrete Subjected to Deicing Salts Cyclic Exposure

Transport Properties of Concrete Subjected to Deicing Salts Cyclic Exposure

Role of sample conditioning in water absorption tests

Abstract Minimizing fluid transport properties of concrete is very important for providing prolonged durability of concrete structures. Sorptivity testing is an easy and effective method for evaluation of near-surface transport properties of concrete. In the sorptivity test, the moisture content of the tested sample has a dominating effect on the rate of absorption. Thus, the drying procedure during sample preparation is an important part of sorptivity testing. In the literature, many different procedures for sample preparation can be found, ranging from long room temperature drying to oven drying at 105 °C for 24 h. In this research, the effect of two drying procedures was compared: a milder one (ASTM C1585 ), and a more rigorous drying (DIN 52617). The comparison was performed on mortars with water to cement ratios of 0.35, 0.40, 0.45, and 0.50, as well as mortars at the water to binder ratio of 0.40 with different levels of cement replacement by fly ash and slag. The initial sorptivity obtained after these drying procedures was compared to chloride migration coefficient and conductivity test results, while the secondary sorptivity was compared with the total porosity. The latter procedure was found to give better correlations with other transport properties of mortars.

Improving the hardened and transport properties of perlite incorporated mixture through different solutions: Surface area increase, nanosilica incorporation or both

Abstract This study investigates the effect of the synergetic incorporation of perlite powder and nanosilica (NS) on mechanical and transport properties of mortar. Inherently, perlite possesses a slow pozzolanic activity, which can prolong the improvement in mechanical and transport properties of concrete. As such, in this study, perlite powder was ground to fine particles with the specific surface area (SSA) of 3100 cm2/g and 3900 cm2/g and was added to the mixture with 10% and 15% replacement level, respectively. Moreover, NS, which is found to accelerate the pozzolanic reaction in cement matrix due to the high surface area, with dosage of 1%, 2%, 3%, and 4% was added to the mixtures in conjunction with the ground perlite to further overcome the slow reactivity of perlite at early ages and improve mechanical and transport properties. The compressive strength of the samples was assessed, and it was found that 15% replacement of Ordinary Portland Cement (OPC) with perlite, with the SSA of 3900 cm2/g, and 2% NS led to the highest compressive strength of 68.3 MPa. Transport properties such as electrical resistivity, rapid chloride migration, and capillary water absorption of the samples were assessed. It was observed that the mixture with 2% NS and 15% replacement of OPC with perlite could increase the electrical resistivity to 35.2 kΩ·cm and reduce the migration coefficient to 4.1*10−12 m2/s at 91 days. Moreover, this mixture decreased the water absorption at 28 days to the extent of 43% in comparison with the control mixture.

Activation Energy of Conduction for Use in Temperature Corrections on Electrical Measurements of Concrete

Abstract The formation factor obtained through electrical resistivity measurements is becoming a popular method to determine transport properties of concrete. Resistivity measurements are dependent on multiple factors, including degree of saturation, pore solution conductivity, and temperature. The Arrhenius equation is used to correct electrical resistivity for temperature effects using an activation energy of conduction (Ea-cond). This parameter has been measured on a wide variety of materials, including pore solutions, pastes, mortars, and concretes (with a variety of saturation states). The reported values of Ea-cond typically range from 9 to 39 kJ/mol. This article examines the factors affecting Ea-cond in order to select an appropriate temperature correction. In this study, Ea-cond was determined from data measured on various concrete mixtures used in transportation infrastructure applications as well as extracted and simulated pore solutions. The Ea-cond of pore solutions remains relatively constant (an average value of 13.9 ± 1.5 kJ/mol) for typical pore solutions and was slightly lower than the Ea-cond of saturated specimens (an average value of 15.8 kJ/mol). It was found that Ea-cond increases as the degree of saturation of the specimen is reduced. Drying increases the ionic concentration of the fluid in the pores; however, this does not explain the changes in Ea-cond. The effects of drying were determined to be primarily due to a change in the volume of the conductive fluid film in the concrete and in the connectivity of the fluid-filled pores. While it is better to directly measure the Ea-cond of a concrete mixture, this is not always feasible or practical. In such cases, for pore solutions, a value of 13.9 kJ/mol can be used, and for saturated concretes, a value of 15.8 kJ/mol can be used. For concretes with a varying degree of saturation, the Ea-cond can be estimated using the developed equation.

Experimental study on the interfacial behavior of normal and lightweight concrete

DOI: 10.7764/RDLC.18.3.476 The interface between aggregate and mortar or paste is a weak phase. This has a serious effect on the properties of concretes. Because of the high porosity of lightweight aggregate, the interface of lightweight concrete is different from that of normal weight concrete. In this study, the effect of interfacial interactions between lightweight aggregate and mortar on the mechanical and chloride ion transport properties of concretes was investigated. The test variables were the volume fraction of the lightweight aggregate and the water–cement (W/C) ratio. The elastic modulus, the electrical charge passed from the rapid chloride penetration test (RCPT), and chloride ion penetration depth were determined. In addition, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were used to observe the microstructures of the interfaces. SEM observation of the lightweight concrete revealed that the interface bonding between mortar and aggregate is considerably firmer than that of normal weight concrete. However, test results indicate that the ability of the lightweight concrete to resist chloride ion intrusion is worse than that of normal weight concrete. Comparison with theoretical models reveals that a negative factor affects the chloride ion transmission in lightweight concrete. As the volume fraction of lightweight aggregate increased, this negative influence is also increased. Chloride ions were detected both in the mortar and the lightweight aggregate in the EDX test. This indicates that chloride ions passed through the lightweight aggregate during the RCPT and can thus influence chloride ion transmission throughout lightweight concrete.

Effects of Fly Ash on Mechanical Properties of Concrete

Abstract Cement is a common and widespread building material over the world. Similarly, carbon dioxide emissions have been significantly increased due to cement production. Alternative low-carbon binders rather than cement have been progressively sought in recent years. Fly ash was found as an available option, since it is being largely disposed annually as a waste material. In this research several studies have been reviewed and recent applications of fly ash on concrete specification, including strength and fracture toughness of green concrete have been perused. Furthermore, transport properties of high volume fly ash after exposure to high temperature and influence of curing temperature on strength development of fly ash-recycled concrete aggregate blends have been investigated. The investigated test results showed that the properties of composites incorporating fly ash depend on the age of the concrete. Test results also revealed that transport properties of concrete increased notably after exposure to 400cº and the results achieved on fly ash-recycled concrete aggregate led to the conclusion that 15% FA is the optimum blend for road stabilization applications.

Strength and transport properties of concrete with styrene butadiene rubber latex modified lightweight aggregate

This experimental work aims to explore the effect of adding SBR (styrene-butadiene rubber) polymeric latex in lightweight aggregates and to study their impact on the concrete. Usually, the SBR is used for precast works and repair works which improve mechanical properties and durability of concrete structures. In this paper, SBR modified lightweight aggregate (SLWA) and normal lightweight aggregate (NLWA) without SBR addition were prepared by palletization process and hardened by cold-bonding technique. The cement (20%) as a binder with fly ash (80%) had been used. The compressive strength, water sorptivity, chloride ion permeability and water permeability tests were performed on SBR added lightweight aggregate concrete (SLWAC). Also, their results were compared with normal lightweight aggregate concrete (NLWAC) of similar composition. In addition to that, fly ash (FA) was partially substituted with natural sand (NS) in concrete. SEM images confirmed the refinement in the microstructure of SLWA. Results revealed that SLWAC presented better desirable outcome than NLWAC owing to higher open porosity and lesser strength of the NLWA respectively. Moreover, it was observed that a considerable enhancement in the strength and transport properties of concrete was achieved by the addition of FA as the partial substitution of the NS.

Modeling the effects of microcracks on water permeability of concrete using 3D discrete crack network

In order to better understand the transport mechanism associated with the microstructural heterogeneity of cracked concrete composite, a modeling scheme is proposed and employed to assess the effects of microcracks on water permeability of concrete. Numerical samples containing 3D discrete crack network (unpercolated and percolated) with different geometric parameters (including crack density, width, length and roughness) are generated to represent the cracked concrete composite, and the effective permeability is estimated using finite element method (FEM). Extensive numerical simulations for more than 8600 concrete samples are carried out to extract the effects of microcracks on the water permeability. The results indicate that crack percolation is a determinant factor for increasing the transport properties of concrete. In addition, for concrete composite with unpercolated crack network, the influential factors to water permeability are crack density and length, while the effect from crack width is negligibly small; and for the percolated case, crack density, width and roughness are more closely correlated with the permeability of cracked composite.

Synthesizing super-hydrophobic ground granulated blast furnace slag to enhance the transport property of lightweight aggregate concrete

This paper studies the feasibility of synthesising super-hydrophobic ground granulated blast furnace slag (GGBS) as water-resisting admixture in lightweight aggregate concrete. The super-hydrophobic GGBS was produced through a ball milling method using the low cost stearic acid. Results show that optimum synthesis involves dry milling stearic acid for 0.5 h with the dosage of 1 wt%, producing a super-hydrophobic GGBS that shows a water contact angle of 155.7°. The morphology, crystalline structure, functional group and chemical state of the atoms were investigated employing SEM, XRD, FTIR and XPS. TEM analysis shows that the thickness of the stearic acid coating is 7.1 nm, confirming the theoretically calculated value. Lightweight aggregate concretes are designed applying an optimized particle packing theory and the effects of super-hydrophobic GGBS on cement hydration, workability, fresh density, strength and transport properties of the concrete are evaluated. Moreover, the relationship between the super-hydrophobic GGBS and the transport properties related performance of the lightweight concrete is discussed. With the addition of the super-hydrophobic GGBS, the capillary water absorption and long-term chloride penetration depth of the LWAC reduce up to about 90%.

Long-term neutron radiation levels in distressed concrete biological shielding walls.

Neutron radiation can deteriorate mechanical properties of the concrete materials, and thus it is questionable that neutron transport properties of concrete can remain unchanged during the life span of biological shielding walls. one-speed neutron diffusion equation and heat conduction equation were used as governing equations for prediction of neutron radiation and thermal field in concrete, respectively. The potential variations of transport properties due to neutron radiation and elevated temperature were estimated. A simplified example of a typical concrete biological shielding wall was analyzed up to 80 years, and the results were discussed. The radiation damage and radiation heating lead to minor changes of the temperature profile in the concrete. However, neutron radiation and elevated temperature can result in considerable increases of neutron flux and fluence in the concrete. The damage of concrete induced by neutron radiation and elevated temperature can considerably accelerate the penetration of neutron radiation into the concrete. This work is the first attempt to deal with the degradation of neutron and heat transport properties of concrete and its effect on neutron fluence distribution in concrete, and provides a possible way to determine the long-term neutron and thermal fields in concrete biological shielding walls.

Production and performance of alkali-activated cold-bonded lightweight aggregate in concrete

The research paper presents the strength and transport properties of concrete produced with alkali-activated cold-bonded lightweight aggregate (CLWA). The CLWA was prepared by the process of pelletization and was solidified (curing) by cold bonding method (ambient room temperature). The cold-bonding technique (at ambient temperature) is considered to be the best cost-effective approach to harden the CLWA with very less energy consumption as compared to sintering technique (which requires more than 1000 °C heat). The fly ash (80%) and cement (20%) with alkali activators (NaOH and Na2SiO3) were used to prepare CLWA. The addition of alkali activators in CLWA decreases the water absorption and increases the crushing strength. Moreover, to know the effect of fly ash (FA) on the strength and transport properties of cold-bonded lightweight aggregate concrete (CLWAC), the sand was partially replaced with the FA and their results were compared with normal weight concrete (NWC) of equal composition. Experiments were conducted on concrete to study the compressive strength, water sorptivity, chloride ion permeability and water permeability. The NWC exhibited better strength than CLWAC due to higher open porosity and lesser strength of CLWA. The scanning electron microscopy images presented the pore structure of CLWA and concrete. The remarkable improvement in strength and transport properties of concrete was observed (CLWAC & NWC) due to an addition of FA as a partial substitution of the sand. This value-added effect can encourage high volume utilization of FA in concrete.