Construction and Building Materials
Volume 299,
13 September 2021
, 123964
Author links open overlay panel, , ,
Abstract
Electrical resistivity shows promise in predicting the mass transport of ions in concrete. This could be of great value because of the low cost, speed, and convenience of performing electrical resistivity measurements. This study uses the Nernst-Einstein equation to correlate the apparent iodide diffusion coefficient (Dic) of fly ash–cement paste and the surface electrical resistivity (ρsr) of fly ash concrete of the same age. This relationship is investigated at three different ages for 19 different fly ash sources at 20% and 40% fly ash replacement to the cement. A factor K which shows the correlation between ρsr and Dic is calculated using the Nernst-Einstein equation, and the relationship is evaluated with a regression analysis. While different K factors were found to relate ρsr and Dic, it was not possible to only use one K factor to relate Dic and ρsr for 20% or 40% replacement of fly ash for the materials and mixtures investigated. Despite there not being a single relationship, this work suggests a practical approach to use the ρsr in a specification to obtain a Dic of the desired value or lower.
Introduction
The mass transport of deleterious ions into concrete can significantly affect the lifespan of concrete structures. The resistance of concrete against ion ingress is one of the most important factors for designing durable concrete structures [1], [2], [3]. Furthermore, the degradation mechanism in reinforced concrete due to chloride-induced corrosion in reinforced concrete can cause several structural problems such as cracking, spalling, and delamination of concrete cover. Previous studies have employed the apparent diffusion coefficient (Dc) as one of the primary parameters to predict the time to corrosion initiation of the reinforcing steel in concrete [4], [5], [6]. Service life prediction models such as Life-365 and DuraCrete predict the initiation period to corrosion assuming diffusion to be the dominant mechanism [7], [8]. There are many papers describing this approach [9], [10], [11], [12]. Thus, Dc is a useful tool to evaluate the service life of concrete structures. The current work focuses on estimating the Dc in fly ash concrete through the surface electrical resistivity of concrete.
Fly ash has been widely used as a supplementary cementitious material (SCM) in concrete to improve the durability of concrete. The incorporation of fly ash in concrete can significantly reduce the Dc value [13], [14], [15]. The chloride penetration has also been evaluated by accounting for the chloride binding for the cement paste using fly ash [16], [17], [18]. Specifically, Thomas et al. [16] studied one Class C and one Class F fly ash with a 25% replacement rate of cement paste. In addition, Qiao et al. [17] investigated the chloride binding of the cement paste for 20%, 40%, and 60% replacement rates of Class C fly ash while Ishida et al. [18] used a Class F fly ash at 20% and 40% replacement rates to examine the chloride binding. These publications found that while fly ash does affect the chloride binding capacity of the cement paste, the chloride binding is not significantly impacted by the fly ash source or the replacement rate when the chloride concentration is around 1.0mol/L in the concrete or less [16], [17], [18]. Because of this, the salt concentrations in this study are limited to 0.6mol/L.
Recent studies employ electrical resistivity techniques to improve the estimation of the Dc of concrete [4], [19], [20], [21], [22], [23]. These efforts have used the Nernst-Einstein equation to investigate the interrelationship between the electrical resistivity and the Dc [1], [5], [24], [25]. The Nernst-Einstein equation is a helpful approach to predict Dc since this equation applies to electrolytes, this can be compared to electrical charges [21], [26]. However, studies in the literature have mainly focus on studying concrete with only one or two types of fly ash. This limited variation in the fly ash chemistry makes it challenging to draw strong conclusions about the usefulness of using the Nernst-Einstein equation to predict the Dc from electrical resistivity measurements. Because of this, a study is needed with a large and diverse number of fly ashes of varying chemical composition by applying the Nernst-Einstein equation.
In this study, an approach using transmission X-ray microscopy (TXM) is applied to examine the Dc for a cement paste containing fly ash. This technique is useful as it is non-destructive and rapid to determine the apparent Dc and surface concentration (Cs). This approach has been presented in previous studies to image the movement of the ions in concrete materials using a potassium iodide (KI) solution as a tracer or contrast agent [27], [28]. The current work investigates the apparent iodide diffusion coefficient (Dic) in cement pastes as the pore structure of the cement paste matrix is related to the ion diffusion in concrete [29]. Moreover, using cement paste is helpful to minimize intervention from aggregates [28], [30]. The surface electrical resistivity (ρsr) is also investigated in the current study for the fly ash concrete by using the four-point Wenner probe measurements as per AASHTO T 358 [31]. In all of this work, the term Dic and ρsr will refer to the apparent iodide diffusion coefficient of the paste and the surface electrical resistivity of the concrete, respectively.
This study aims to evaluate the possibility of determining Dic using ρsr in concrete materials including fly ash and provides insights into the relationship between Dic and ρsr for 20% and 40% fly ash replacement levels at 45d, 90d, and 135d by using the Nernst-Einstein equation. This provides important insights into the relationship between electrical resistivity and Dc in concrete structures.
Section snippets
Raw materials
ASTM C150 Type I ordinary portland cement (OPC) [32] was used as a cement, and the properties of the OPC are described in Table 1. For the samples of fly ash concrete for the surface electrical resistivity measurements, limestone and natural sand from Oklahoma were prepared as coarse and fine aggregate, respectively. The specific gravities of the coarse and fine aggregate were both 2.60, and the absorption for each aggregate is 0.64% and 0.55%, respectively. No chemical admixtures were used in
Bulk chemical composition
Table 4 shows the bulk chemical composition result from the ASEM method for nineteen fly ash sources used in the mixtures. The fly ashes with “C#” represent Class C fly ash while the fly ashes with “F#” represent Class F fly ash. All the fly ashes are classified as either Class C or F fly ash according to ASTM C618 (Class C fly ash has>18% of CaO while Class F fly ash has<18% of CaO [33]).
Change in ρsr over time
Fig. 1 shows the ρsr over time for the samples investigated in this work at 20% and 40% fly ash
Conclusions
The present work employs the Nernst-Einstein equation to investigate the empirical relationship between the electrical surface resistivity and apparent diffusion coefficient for 20% and 40% fly ash replacement in concrete mixtures for 45d, 90d, and 135d of hydration. This study shows that an accurate prediction of the apparent diffusion coefficient is reasonable for practical applications.
The accuracy was examined by developing a predictive equation and then determining the percentage of data
CRediT authorship contribution statement
Shinhyu Kang: Conceptualization, Methodology, Software, Validation, Formal analysis, Investigation, Resources, Data curation, Writing - original draft, Visualization, Writing - review & editing. Zane Lloyd: Methodology, Investigation, Data curation, Validation. Amir Behravan: Methodology, Investigation. M. Tyler Ley: Conceptualization, Methodology, Validation, Investigation, Writing - review & editing, Supervision, Project administration.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This work was sponsored by funding from the Illinois Department of Transportation [Project ICT R27-180], and the FHWA [EAR project # BAA No. 693JJ3-18-BAA-0001]. The authors would like to thank Dr. Daniel Cook for the assistance and discussion of this work.
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Cited by (5)
Performance and prediction of non-traditional coal-ash in concrete with the Particle Model
2022, Construction and Building Materials
Citation Excerpt :
The compressive strength is a widely used parameter for the design of concrete structures, and surface resistivity is a useful indicator for the reaction of the concrete over time [3,4,13,15]. The surface resistivity measurement can also provide useful insights into the ability of the concrete to resist ion penetration into the concrete if the concrete is correctly conditioned [15–17]. Therefore, this work can provide useful insights into the performance of NTCA as well as the ability of the Particle Model to predict their performance in two widely used tests.
The demand for non-traditional coal ash (NTCA) such as ponded ash, landfilled ash, ground bottom ash, and blended ash in concrete is increasing because of the reduction of the total production of traditional fly ash in the US. In this work, 11 different NTCA sources are used for concrete mixtures. The compressive strength and surface resistivity of NTCA concrete is measured at 7 different times of hydration between 3d and 180d at 20% and 40% replacement levels. This study shows that NTCA shows similar properties and performance to traditional fly ash. Next, a predictive model for compressive strength and resistivity based on traditional fly ash is used to predict the performance of NTCA concrete. The developed predictive models for traditional fly ash show promise for predicting the compressive strength of NCTA fly ash at 20% and 40% replacement but surface resistivity models need improvement.
(Video) Mechanical Properties and Electrical Resistivity of Portland Limestone Cement Concrete SystemsAlternative small-scale accelerated test to measure the effect of thermal shock on rendering mortar properties
2022, Journal of Building Engineering
Citation Excerpt :
All six mortars showed this same trend. The electrical resistivity of the mortars was reduced (Fig. 12a) with the thermal shock test, since this property is an indirect measure of the quantity and connectivity of the material's pores, being an important parameter to measure the mass transport properties and the degree of degradation of cement composites [42–44]. The dynamic modulus of elasticity test allows the assessment of the existence of internal cracks [45,46] in the material since it is performed through the propagation of ultrasonic waves.
This article proposed an alternative small-scale accelerated test to measure the effect of thermal shock on rendering mortar properties. First, the temperature variation during the heating and cooling period was analyzed. Furthermore, two cooling setting conditions were evaluated. The final configuration of the accelerated test was applied to six mortar mixtures after 28 days of curing. The main property affected by the thermal shock was the length change of prismatic specimens. The other properties (capillary coefficient, tensile and compressive strengths, dynamic modulus of elasticity, and electrical resistivity) of the rendering mortars were affected by about 10%–30%. The thermal expansion coefficients found were consistent with the literature. Also, the tensile thermal stress values estimated from a theoretical model were greater than the tensile strength values of the mortars, indicating the tendency of internal cracking of the material.
Contribution to the service-life modeling of concrete exposed to sulfate attack by the inclusion of electrical resistivity data
2022, Construction and Building Materials
Citation Excerpt :
Low R2 has also been found by Andrade et al. [24]. Kang et al. [21] found R2 around 0.6 for tests using a potassium iodide solution as an external ion. However, this solution does not react as much with the cement paste as is the case with the sodium sulfate solution.
The objective of this study was to explore the modeling of the external sulfate attack (ESA) using electrical resistivity data as an input parameter of the equations. An extensive experimental program was designed to relate the sulfate diffusion coefficients to the electrical resistivity of concrete. For this purpose, concrete specimens were cast and exposed to wetting and drying cycles in sodium sulfate solutions for 140days. Sulfate profiles were determined after 28, 56, 112, and 140days of exposure. The diffusion coefficient was determined by Fick’s law of diffusion. The well-known Einstein relation between the diffusion coefficient and the electrical resistivity was tested and two existing service-life models from the literature were adjusted with the inclusion of electrical resistivity to predict the entry of sulfates into concrete. Results indicated a negligible prediction error varying around 7%.
Chloride Penetration Resistance, Electrical Resistivity, and Compressive Strength of Concrete with Calcined Kaolinite Clay, Fly Ash, and Limestone Powder
2023, Journal of Materials in Civil Engineering
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FAQs
What is the effect of fly ash on concrete? ›
Fly ash use in concrete improves the workability of plastic concrete, and the strength and durability of hardened concrete. Fly ash use is also cost effective. When fly ash is added to concrete, the amount of portland cement may be reduced. Benefits to Fresh Concrete.
How do you calculate fly ash percentage in concrete? ›- Volume of concrete = 1m^3.
- Volume of cement = (285 / 3.15) x1/1000= 0.090 m^3.
- Volume of fly ash = ( 122/2.2) x1/1000=0.055 m^3.
- Volume of water = ( 149/1)x 1/1000=0.149 m^3.
- Volume of admixture = ( 7.6/ 1.145)x1/1000=0.006 m^3.
- Volume of coarse aggregate and fine aggregate = a – ( b + c + d+
Fly ash particles are spherical and are smaller in size than cement. Fly ash can only be activated when cement is being used as well. When cement reacts with water, it produces lime, which reacts with fly ash, which produces CSH (Hydrated Calcium Silicate). The CSH is the same cementing product as Portland cement.
What is the ratio of fly ash to concrete mix? ›| Total cementitious | wt. (kg/m3) |
|---|---|
| Fly ash= 482 x 0.30 = 145 | 145 / 2250 |
| Water (free) = 170 x 0.95 = 162 | 162 / 1000 |
| Superplasticizer= 482 x 0.01 = 4.82* | 4.82 / 1150 |
| Air = 1% |
With the addition of fly ash, the chloride permeability of concrete is in a low category. With the addition of fly ash, the chloride permeability is reduced by 82, 61, 48 and 41% of control samples respectively, for concrete with 10, 20, 30 and 40% of fly ash content.
What are major influences of fly ash on concrete properties? ›Fly ash is a by-product material obtained from the combustion of coal. It is used as pozzolanic material in mortar and concrete, and has demonstrated significant influence in improving the properties like water requirement, workability, setting time, compressive strength, durability of mortar and concrete.
What is the formula of fly ash? ›SiO2, Al2O3, Fe2O3 and occasionally CaO are the main chemical components present in fly ashes. The mineralogy of fly ashes is very diverse. The main phases encountered are a glass phase, together with quartz, mullite and the iron oxides hematite, magnetite and/or maghemite.
What is the compaction percentage of fly ash? ›The difference of the OMC and MDD of Fly Ash (collected from NTPC kanhia, Odisha) according to the standard proctor compaction energy is 0.90 – 1.59 gm/cc and 18 - 27%, respectively.
What is the disadvantage of using fly ash? ›The quality of fly ash can affect the quality and strength of Cement concrete. Poor-quality fly ash can increase the permeability of the concrete and cause damage to the building.
Does fly ash increase compressive strength of concrete? ›The compressive strength of concrete decreases with increase in fly ash content. The reduction in compressive strength of concrete at the age of 28 days was found to be 4.57%, 12.20% and 20.55% for 10%, 20% and 30% replacement of cement with fly ash.
Is fly ash stronger than concrete? ›
The reduction in water leads to improved strength. Because some fly ash contains larger or less reactive particles than portland cement, significant hydration can continue for six months or longer, leading to much higher ultimate strength than concrete without fly ash.
What is the limitation of fly ash in concrete? ›However, using fly ash in concrete does come with potential problems. Substituting fly ash for Portland cement in a concrete mixture leads to longer drying and curing times. When used in cold climates, mixtures with high levels of fly ash can also encounter issues with slow strength development.
What is the maximum fly ash in concrete? ›One contributor indicated that on the factors related to durability-or more specifically, deicer exposure both ACI 318-99 and the International Building Code limit the maximum fly ash content to 25% if the concrete will be exposed to deicing chemicals.
How strong is high volume fly ash concrete? ›The results show that HVF A concretes exhibit excellent mechanical properties ",ith good long-term strength development. Compressive strength in the range of 40 to 60 MPa "as achieved for all the HVF A concretes at the age of 90 days.
Is fly ash good or bad for concrete? ›Fly ash makes concrete workable; increasing its levels may reduce water demand and superplasticizer needs. Fly ash can improve mechanical and durability parameters of concrete. Fly ash concrete can perform better against chloride, sulfate and acid attacks and can improve corrosion resistance.
Is fly ash safe in concrete? ›Recommended Use: Fly ash can be used as supplementary cementitious material for concrete, cement additive, mortar additive. It may also be used in road soil stabilization processes and as asphalt filler.
Does fly ash make concrete lighter? ›The use of flyash as coarse aggregates resulted in the reduction of density of concrete by 15% when compared with conventional concrete. This reduction in density was due to the light weight of flyash aggregates.
Is fly ash in concrete toxic? ›Since fly ash is a by-product of coal combustion, it often contains the harmful elements of the burned coal. Fly ash may have trace amounts or even higher levels of known health hazards such as lead and mercury.