Water-cementitious Material Research Articles

Assessment of corrosion prevention methods for steel reinforcement embedded in concrete exposed to a natural marine environment

Corrosion of the steel reinforcement is a serious problem that lessens the durability of concrete structures. Numerous research studies focus on the improvement of the concrete matrix and the protection of the reinforcing bars against corrosion. Fly ash and silica fume have been used for the former and inhibitors for the latter; nevertheless, corrosion is a very complex multifactorial phenomenon because the deterioration mechanisms involved in a simulated-marine environment differ from those involved in a natural environment. Despite these facts most corrosion studies have been carried out in a laboratory under accelerated conditions and using non-destructive testing. In this research, the effects of the water-cementitious materials ratio, fly ash, and a calcium nitrite-based corrosion inhibitor, as well as their interactions, were investigated as methods to prevent the corrosion of reinforcing steel in concrete containing silica fume. Specimens were exposed to a natural marine environment for seven years and the corrosive activity was monitored annually using electrochemical techniques. At the end of the exposure period, the specimens were visually inspected, autopsied and the chloride concentrations at the steel–concrete interfaces were estimated. The steel bars were extracted and their mass losses and pitting depths evaluated and finally tested for tension. The results show the underlying performance of fly ash, alone or in combination with CNI, improves the concrete matrix and is an effective corrosion prevention method.

Mass Concrete Mixtures Optimized for Temperature Control and High Workability

Mass concrete is prone to thermal cracking, deleterious chemical reactions, and ultimate strength reduction caused by a high temperature rise. Defining mass concrete has been difficult since many factors affect the thermal behavior and the distress formation. Mass concrete is usually reinforced and may have geometric constraints that require concretes with high workability, as with self-consolidating concrete. For high workability and strength, high amounts of cementitious material are used for stability and low water–cementitious material ratios. Such amounts generally cause high water and paste contents that lead to cracking because of moisture loss and thermal contraction. In this study, a practical and useful definition of mass concrete was explored. Concretes with low cementitious material contents and high workability were investigated. To minimize the total cementitious material and paste contents, optimum aggregate gradations were considered. To achieve and maintain high workability during construction, a combination of admixtures was used that included high-range water reducing, workability-retaining, and viscosity-modifying admixtures. Laboratory testing of concretes with reduced cementitious material contents including high amounts of the supplementary cementitious materials and a combination of admixtures showed that concretes with a decreased temperature rise, high workability, and adequate strength can be obtained.

Effect of additional water or superplasticizer on key characteristics of cement paste made with superabsorbent polymer and other shrinkage mitigating materials

The use of superabsorbent polymer (SAP) coupled with expansive agent (EA) or shrinkage-reducing admixture (SRA) can effectively reduce shrinkage of cement-based materials. However, SAP particles at high contents can adversely affect rheological and mechanical properties. Securing proper workability can be accomplished by additional water or adjusting the superplasticizer (SP) demand. There is an uncertainty about the efficiency of these approaches to workability compensation. This study evaluates the effect of additional water or SP on key properties of cement paste made with SAP and relatively high content of EA or SRA. Macro and micro mechanisms underlying the effect of combined shrinkage mitigating strategies on the performance of cement paste made with 0.4 water-cementitious materials ratio are investigated. Results indicate higher efficiency of increasing SP demand by 0.6% versus the addition of water by 30 g per gram of SAP. Up to 80% higher compressive strength is obtained for the mixtures made with additional SP, which is attributed to up to 33% reduction in capillary porosity and smaller pore-size distribution of the hydrated cement paste. In the presence of high EA content, the use of additional SP prevents excessive initial expansion in the paste with additional water.

Mix design and characteristics evaluation of high-performance concrete with full aeolian sand based on the packing density theory

• A newly high-performance concrete was prepared by using aeolian sand. • The modified Andreasen & Andersen model was employed to determine the volume fractions of solid powders. • The optimization values of W/C, SP and FA content are 0.19, 1.0 and 25.86 respectively. • The internal pores of developed FAS-HPC are harmless and the pore porosity is 7.3%. • This study further enriches the raw materials for HPC and proposes a fully calculated design method. To solve the shortage issue of high-quality construction aggregates in desert areas and improve the utilization rate of aeolian sand, this study introduces the mix design and characteristics evaluation of high-performance concrete with full aeolian sand (FAS-HPC). The modified Andreasen & Andersen model is employed to determine the volume fractions of solid materials when the mixture system reaches the best packing density. Then the Response Surface Method (RSM) is utilized to conduct the orthogonal design and evaluate the effect of water-cementitious materials (W/C), superplasticizer (SP) and fly ash (FA) content on the flowability, mechanical properties, shrinkage and impermeability of the developed concrete, thus the raw materials proportion of FAS-HPC is optimized. After that, the pore structure and microstructure of the developed concrete are tested and analyzed to verify its durability and compactness. The results show that the volume fractions of AS, silica fume, and cement are determined as 0.482, 0.093, and 0.425 respectively, and the introduction of FA is found to be effective in improving the fluidity and impermeability while reducing the early strength and shrinkage. Under the determined response goals, the optimal values of W/C, SP and FA content are 0.19, 1.0 and 25.86 respectively. While the developed FAS-HPC formed by this ratio has a flowability of 220 mm, 28d flexural strength and compressive strengths of 20.26 MPa and 97.09 MPa respectively, meeting the requirements of HPC. Additionally, the developed FAS-HPC has a porosity of 7.3 % and 76.4 % pores are harmless, which can ensure its superior chloride resistance and durability. This study further enriches the raw materials for HPC and proposes a fully calculated design method, which is of great significance to the sustainable development of HPC.

Assessing the critical chloride threshold of conventional reinforcement embedded in alternate cementitious systems

Alternate cementitious materials (ACMs), such as calcium aluminate cements (CAC) and calcium sulfoaluminate cements (CSA), contain lower embodied energy and carbon footprints when compared to traditional ordinary portland cement (OPC) systems. However, the sustainability of these ACM systems can be nullified by a lack of durability and/or resiliency. To develop an understanding of the durability and long-term performance of the ACMs, standardized test methods are required to assess their corrosion resistance. OCcrit, a new test method that was developed at Oregon State University, is a fast and reliable method to study the corrosion performance of cementitious systems. This method, however, has only been evaluated using OPC systems. In the first part of this study, testing was performed to potentially extend the applicability of this new test method to CAC and CSA systems, thereby increasing its robustness and value. In the second part of the study, the updated OCcrit method was used to assess the critical chloride threshold of steel reinforcement embedded in CAC and CSA systems. Results indicate that CSA specimens exhibit lower critical chloride threshold values than OPC and CAC specimens and the critical chloride threshold of the CAC seems to be dependent on the water-cementitious materials ratio.

Mechanical properties and electrical resistivity of portland limestone cement concrete systems containing greater than 15% limestone and supplementary cementitious materials

This investigation explored the feasibility of producing strong, good quality, durable concrete in low-clinker systems (less than 50% clinker in some cases). The low-clinker content was achieved by combining interground portland limestone cement (PLC) with high limestone contents and different supplementary cementitious materials (SCMs). Seven cements, with approximate limestone contents between 3% and 31%, from two cement plants were used, in combination with SCMs, in forty-two different mixtures with water-cementitious materials ratios (w/cm) of 0.40 and 0.45. The SCMs included Class F and C fly ashes, Grade 100 slag, and silica fume. Mechanical properties (compressive strength, tensile strength, elastic modulus) and electrical resistivity were measured at 1, 7, 28, and 91 days. Similar compressive strengths were observed for mixtures with equivalent effective w/cm ratios. Although, the combination of PLCs with SCMs for very low-clinker systems resulted in decreased compressive strength, an increase in electrical resistivity was observed. More importantly, strong, good-quality concrete can be produced without sacrificing environmental benefits.

Augmentation of Abrams law for fly ash concrete

Abrams law which was formulated for conventional concrete containing cement as the only cementitious material, might not be directly applicable for concrete containing present day mineral admixtures. The present study deals with mathematical models using statistical methods relating compressive strength to a number of parameters affecting it, like water binder ratio, fly ash to binder ratio, fly ash content, cement content etc. The importance of the proposed equations has been evaluated by combination of the parameters one by one or by combination with more than one parameter. These models might serve as useful tools in the modification of Abrams law for fly ash concrete. The present research work has been directed towards general concrete construction involving low to medium strengths, no superplasticizer has been used and the mix design methodology has been kept as simple as possible. The water cementitious material ratios ranged from 0.4 to 0.6 and cement was replaced by fly ash @ 0, 20, 30, 40 and 50 percent of the weight of cementitious material. Cementitious material contents ranged between 300 and 450 kg/m3.

Compressive strength of SF and FA based self curing HSSC: An experimental study

Typical High-strength concrete (HSC) mixtures are characterized by low water-cementitious material ratio, high content of cementitious material, and the incorporation of admixtures. Concrete needs a favourable atmosphere by providing moisture for a minimum base period of 28 days for hydration and to attain targeted strength. In the present scenario of water scarcity, the water required for curing concrete is a troublesome constraint. Self-curing concrete is one of the peculiar concretes for coping with insufficient curing caused by human error. The prime goal of this study is to identify the self-curing compound’s optimum dosage for High Strength Self-Compacting Concrete (HSSC). Likewise, it is aimed to investigate the compressive strength characteristics of HSSC. For the study, a self-curing agent namely “PEG-400” with varying percentages (0.5%, 1%, 2% & 3% by weight of cement) was investigated. An attempt was made to identify the effect of the self-curing compound on the fresh and hardened properties of HSSC, workability tests and compressive strength tests were conducted. The tests on hardened concrete were conducted after curing for 28 days for conventional HSC specimens and ambient curing for HSSC. It was observed that with the addition of 1% of PEG-400 self-curing compound, the compressive of HSC was found to be increased by 1.86% in comparison with the conventionally cured HSC. It was observed that with the addition of 1% of PEG-400 self-curing compound, the compressive strength of HSSC was found to be increased by 1.87% in comparison with the conventionally cured HSSC.

Effect of Reclaimed Asphalt Pavement Aggregate on Hardened Properties of Concrete

Abstract: This paper purpose of study is to find the properties of Reclaimed asphalt pavement (RAP) and compare the same with the concrete produced with natural aggregates. This thesis presents a study conducted on mechanical and durability properties of Reclaimed asphalt pavement (RAP) aggregates concrete. The investigation covered concrete mixes at water cementitious material with ratio of 0.4. Ordinary Portland cement of 43-grade was used in this study. The percentage of Reclaimed asphalt pavement (RAP) aggregates that partially replaced natural aggregates by weight were 0%, 25%, 50%, 75%, and 100% with glass fiber The results show that the optimum replacement of Reclaimed asphalt pavement (RAP) with natural aggregate then gain strength of concrete compare with normal mix. It is observed that compressive and tensile strength of concrete gain upto with mix 50% NA+50%RAPA+1%SF after that increase percentage of RAP with decrease both strength compare with normal mix. Keywords: RAP, steel fiber, design mix, compressive strength, split tensile strength.

Engineering Properties and Prediction of Strength of High Performance Fibre Reinforced Concrete using Artificial Neural Networks

ABSTRACT: This paper presents the experimental and numerical studies on high performance fiber concrete (HPFRC) with water-cementitious materials (w/cm) ratios of 0.4- 0.3, steel fiber volume fraction (Vf) varying from 0- 1.5%, polypropylene fiber volume fraction varying from 0- 1% and silica fume replacement at 10% and 15%. Experimental results showed high improvements in 28 day cylinder compressive strength and flex-ural strength of steel fiber reinforced concrete at fiber volume fraction of 1.5%; for polypropylene (PP) FRC improvement in compressive and flexural strengths are marginal and moderate, respectively. Statistical models developed for compressive strength ratios and flexural strength ratios of HPSFRC indicate the prediction ca-pabilities of the models. Due to the complex mix proportions of HPSFRC and the non-linear relationship be-tween the concrete mix proportions and properties, research on HPSFRC has been empirical and no models with reliable predictive capabilities for its behavior have been developed. Based on the large data collected for HPSFRC mixes, a trained artificial neural network (ANN) model which adopts a back propagation algorithm to predict 28-day compressive strength of HPSFRC mixes was employed. This paper describes the comparison of the experimental results obtained for various mixes. Multiple linear regression (MLR) model with R2 = 0.78 was also developed for the prediction of compressive strength of HPSFRC mixes. On validation of the data sets by NNs, the error range is within 2% of the actual values. ANN models give the significant degree of ac-curacy compared to MLR model, and can be easily used to estimate the strength of concrete mixes.

The relationship between curing regime and mechanical properties of controlled low-strength material

This paper outlines research conducted on controlled low strength material (CLSM) to examine the effects of curing condition and water-cementitious material (w:cm) ratio on its engineering properties, including compressive strength, elastic modulus, indirect tensile strength, drying shrinkage, and setting time. Two different curing regimes were used to assess compressive strength and indirect tensile strength. In the first curing regime, continuous curing was applied in a 100% relative humidity environment and at a temperature of 70°F (21.1 °C). In the second, continuous curing was used in a 50% relative humidity (RH) environment at a temperature of 70°F (21.1 °C). Curing the specimen at 50% RH environment remarkably decreased the rate of strength gain when compared to the 100% RH environment. The compressive strength and indirect tensile strength of CLSM, as expected, also increased as the w:cm ratio decreased from 1.0 to 0.8 for the same curing conditions and decreased as the cement amount was lowered in the mix. The bar linear shrinkage tests showed that shrinkage strain at 50% RH decreased when the w:cm ratio decreased. Tests conducted to investigate the effects of curing temperature and w:cm ratio on the setting time showed that CLSM sets faster as curing temperature increased from 50°F (10 °C) to 90°F (32.2 °C) w:cm ratio decreased from 1.0 to 0.8.

Rheology of High-Volume Fly Ash Self-Compacting Recycled Aggregate Concrete

AbstractEffect of selected volumetric replacement (0%, 20%, 40%, and 60%) of cement with class-F fly ash in a binary binder and of three water-cementitious material ratios (0.40, 0.34, and 0.28) on...

A Study on Strength Behavior of High Performance Concrete

High Performance Concrete can be seen of as a natural progression from Cement Concrete, where the elements are balanced and chosen to effectively contribute to the many features of Cement Concrete in both the fresh and hardened phases. One of High Performance Concrete's characteristics that offers important structural advantages is higher strength. Concrete, steel reinforcement, and formwork make up the three main expenses for a structural member. This study compares these important elements when higher-grade concrete is used in the design, with the goal of demonstrating that high strength concrete offers the most cost-effective solution for designing load-bearing members and for carrying a vertical load to the building foundation through columns. The water-cementitious material ratio, total cementitious material, cement-admixture ratio, and amount of super plasticizer dosage are the mix design elements that have the greatest impact on concrete strength. To create a higher-grade concrete mix, these variables need to be examined.

Optimization of Sustainable Concrete Mixes Containing Binary and Ternary Blends

In this research 26 mixes in six different group were studied with three groups for each of the water cementitious material ratios (w/b) of 0.3 and 0.4 and a control mix. The first and fourth groups contained five percentages of silica fume (SF) as partial replacement of cement (5%, 7.5%, 10%, 12.5, 15%) for w/b ratios of 0.3 and 0.4, respectively. The second and fifth groups contained four percentages of Class F fly (FA) ash as partial replacement of cement (10%, 15%, 20% and 25%) for the w/b ratios of 0.3 and 0.4, respectively. The third and sixth groups contained three different percentages of both Class F fly ash and silica fume as partial replacement of cement with SF 5%+ FA 10%, SF 10%+ FA 15% and SF 15%+ FA 20% for w/b ratios of 0.3 and 0.4, respectively. For all of these mixes the compressive strength was first studied then the benefit greenhouse gases (GHG) ratio and Benefit cost ratio were found for all the studied mixes. Two optimization processes were performed during the course of this research, the first optimization process results can be used when the concrete durability is not a concern (concrete durability results are not accounted for). Whereas, the results of the second optimization process can be used when the concrete durability is a concern (concrete durability results are accounted for). The details of the results and the optimization processes are presented in this paper.

Determination of the plastic viscosity of superplasticized cement pastes through capillary viscometers

Determining correctly the rheological parameters of the cement paste is a matter of capital importance when designing a self-compacting concrete (SCC). For this, it is necessary to resort to rheometers, which are expensive and, therefore, not available in all laboratories. However, the measurement of plastic viscosity can also be carried out using capillary viscometers, simple and cheap instruments whose foundation lies in the time it takes for a volume of suspension to flow through the hole in a capillary. It is common practice to use the Marsh funnel in the construction industry but not the Cannon–Fenske viscometer, more used in other industries such as chemistry. Besides, most of the models associated with the Marsh funnel have been developed for drilling muds, although there are some exclusive for cementitious suspensions. However, the rheological nature of both materials is very similar, so it seems appropriate to check how these models behave in cement pastes designed for SCC. Consequently, the rheological behavior of 39 cement pastes of different composition was studied (varying the nature of cementitious materials and the superplasticizer admixture, with various water–cementitious materials ratios) to check the performance of said devices and models using the plastic viscosity measured with a rotational rheometer as a reference. The results indicate that the Cannon–Fenske viscometer offers a better approximation to the reference plastic viscosities than the Marsh funnel. As for the comparison between models for the Marsh funnel, the results obtained are disparate, so it would be convenient to expand the experimental research to adjust the parameters of the models that offer a good approach.

Effect of Moisture Content on the Behavior of High Strength Concrete at High Temperatures

ABSTRACT In this paper, an experimental program was carried out to investigate the residual mechanical properties of high strength concrete and normal strength concrete, and how moisture content and temperature affect the spalling process. Three mixtures with water-cementitious material ratios, from 0.25 to 0.50, and with different saturation levels were heated in an electric furnace to elevated temperatures, from 200°C to 600°C. After heating, the specimens were cooled down to room temperature and then tested for compression and tensile strength. The results showed that high moisture content induces the spalling process and reduces considerably the mechanical properties of high strength concrete, mainly at temperatures above 400°C.

Revised Method for Rapid Determination of On-Site Water–Cement Ratio using Microwave Oven

The water–cement ratio (w/c) of delivered concrete is one of the most important parameters of the material’s quality. In this study, the AASHTO T318-15 guideline was adopted to estimate the water content of fresh concrete mixes and was revised for better precision. The additional step required sieving out the coarse aggregate after drying the sample in a microwave oven, and using it in the calculation of the absorbed water and cementitious material content. The cementitious content was assumed to be proportional to the mix design ratios. Several laboratory batches, as well as on-site water–cementitious material (w/cm) ratio tests, were performed on concrete mixes containing ordinary Portland cement, ground-granulated blast furnace slag, and Class F fly ash. The results of the experiments indicated the accuracy of the revised method was increased to have an average percentage error of about 2.16% from the actual w/cm ratio whereas the method based on AASHTO calculations was 6.2%. For cases with high chemical admixture dosages, washing vinegar was used to wash out the particles around the dried sieved coarse aggregate to calculate the w/cm ratio with a more precise mass for each sample. The correlation between the measured and calculated compressive strength using the measured amount of w/cm ratios provides evidence for the method’s accuracy. Therefore, the revised method can be used as an accurate and practical process of measuring the on-site w/cm ratios of fresh concrete mixes.

Determination of optimum mixture design method for self-compacting concrete: Validation of method with experimental results

This paper describes the mixture design method for self-compacting concrete (SCC) while making use of supplementary cementitious materials (SCMs) for the design of concrete mixture to assess early age strength and self-compactability. The proposed procedure “strength-based mixture design method” also makes use of packing theory to achieve targeted strength, enhanced durability, and minimum paste volume. The factors that primarily influence the strength and durability of concrete are the amount of SCM, cement, and water. Depending on data from past studies, a relationship between compressive strength and the water-cementitious material ratio is introduced in the proposed mixture design method to achieve targeted early age strength. The optimal percentage of SCM for use in concrete was assessed using strength efficiency method. The proposed mixture design method shows that SCC made with an optimal percentage of metakaolin as SCM at W/CM of 0.38, 0.26, and 0.17 achieved the expected strengths of 60, 90, and 120 MPa, respectively, after 28 days of standard curing.

Predicting the degree of reaction of supplementary cementitious materials in cementitious pastes using a pozzolanic test

A pozzolanic test that can correctly identify pozzolanic materials is key in the search for alternative supplementary cementitious material (SCMs). Determination of the degree of reaction of these alternative SCMs in cementitious pastes is also important, as the reactivity of certain SCMs can be quite low. Since typical methods to determine SCM degree of reaction can be complex and laborious, the current study explores whether parameters obtained from a newly developed pozzolanic test can potentially be used to develop a simple method for determining the degree of reaction of SCMs. In the pozzolanic test, (cumulative) heat release and calcium hydroxide consumption of SCMs from a mixture of SCM and calcium hydroxide (water-to-solids ratio 0.9, pH 13.5, and testing temperature of 50 °C) are measured. Corresponding values of cumulative heat release and calcium hydroxide consumption of SCMs in a cementitious paste are also measured at two different water-cementitious materials (w/cm) ratios. The ratio between the values of cumulative heat release and the calcium hydroxide consumption in the cementitious paste and the pozzolanic test are considered to be measures of degree of reaction. Four different SCMs – class F fly ash, ground granulated blast furnace slag, metakaolin, and undensified silica fume were tested in this study. The effect of temperature and w/cm on degree of reaction were assessed. Degree of reaction values obtained from this method were compared with those from obtained from a portlandite consumption method suggested in literature and from typical values suggested in literature. Good correlation (R2 = 0.87) is obtained for the degree of reaction values determined here using the calcium hydroxide ratio and the portlandite consumption method. The degree of reaction values increase as the temperature increases but do not strongly depend on w/cm. The degree of reaction values are in general agreement with the range of values obtained from literature, however, this range is rather large, and the values depend strongly on the method used to determine degree of reaction. These preliminary results are promising and suggest that this method may potentially be used to provide information about pozzolanicity and degree of reaction of various SCMs.

Characteristic and effects of a superplasticizer quantity variation in some concrete strengths optimization

This study investigates the properties of superplasticized concrete and compared results to that of normal concrete. Four different concrete proportioning of 1:2:3 mix ratio have been considered. A0 is normal concrete having 0.4 water cement ratio (w/c) and is the control while A1, A2 and A3 are superplasticized concretes having 0.3 water cementitious materials ratio (w/cm) with varied percentages of the superplasticizer. Beams, cubes and cylinders, 60 each were cast, de-moulded and cured. They were tested for strengths at different days of curing; 7, 28, 56, 90 and 120 days. Appropriate casting of fresh concrete paved way for 60 beams, 60 cubes and 60 cylinders specimens which were subjected to 7, 28, 56, 90 and 120 moist cured days and were duly subjected to strength tests. Tests on the material constituents used for the concrete production showed that they satisfied standard specification requirements. The workability test results on fresh concretes showed that as the dosage of superplasticizer is increasing the values of both slumps and compaction factors are increasing. Significantly, the flexural, compressive and tensile splitting tests results showed that as workability of the fresh concrete is increasing the related hardened concrete strength is also increasing. An improvement in the appearance (smoothness) was observed in the specimens produced as the superplasticizer dosage increases. Keywords: Experimental, Properties, Proportioning, Superplasticizer, Concrete