Robert Spragg

Abstract: A series of wetting and drying tests were performed on concrete using different aqueous solutions containing deicing salts. The rate of fluid absorption was generally lower for aqueous solutions containing deicing salts than it was for water. In addition, less fluid was absorbed for samples exposed to aqueous solutions containing deicing salts than for samples exposed to water. The change in the rate of aqueous fluid absorption was proportional to the square root of the ratio of surface tension and viscosity of the absorbed fluid. Concrete that has been exposed to solutions containing deicing salts showed less mass loss during drying. Measures of equilibrium relative humidity over the salt solutions are used to interpret drying behavior. Experimental data indicates that concretes that had previously been exposed to deicing solutions can also exhibit reduced rate of absorption, even if water is the fluid being absorbed.

Abstract: The electrical resistivity of cement-based materials can be used in quality control or service life prediction as an indicator of the fluid transport properties of these materials. Although electrical tests have the advantage of being easy and rapid to perform, several key factors can influence the results: (a) specimen geometry, (b) specimen temperature, and (c) sample storage and conditioning. This paper addresses these issues and compares the measurements from several commercially available testing devices. First, the role of sample geometry is explained with the use of three common geometries: surface, uniaxial, and embedded electrodes. If the geometry is properly accounted for, measurements from different test geometries result in electrical resistivity values that are similar. Second, the role of sample temperature is discussed for both pore solution and uniaxial tests on cylinders. Third, the paper examines the importance of sample curing, storage, and conditioning. Sample storage and conditioning ...

Abstract: Many agencies are interested in using a rapid test method for measuring the electrical properties of concrete (i.e., the resistivity or conductivity) because the electrical properties can be related to fluid transport (e.g., ion diffusion). The advantage of electrical testing is that it is relatively easy to perform, and the test method is relatively fast (it takes less than a minute). Over the past century, many studies have investigated different approaches for measuring electrical properties. This paper describes the variability associated with measuring the bulk resistivity along the longitudinal axis of a cylinder after placing electrodes on either end. A multi-laboratory evaluation was performed at ten laboratories. Data from this evaluation provided variability data for 12 concrete mixtures at testing ages of 28, 56, and 91 days. Information on the variability is important in the development of precision and bias statements for standard test methods. In addition, this work discusses how the resistivity results obtained from this test can be correlated with surface resistivity measurements made using a Wenner probe. Linear agreement was noticed between the Wenner test and the measurement through the cylinder, but with a factor confirmed by previous research by Morris et al. (“Practical Evaluation of Resistivity of Concrete in Test Cylinders Using a Wenner Array Probe,” Cem. Concr. Res., Vol. 26, 1996, pp. 1779–1787). Additionally, the effect of electrode resistance is discussed, and for high resistivity concrete such as that used in much transportation infrastructure, this effect appears to be negligible; however, it can be accounted for easily.

Abstract: This paper discusses a series of electrical measurements made on cementitious mortars containing water–NaCl solutions (0–23.3% concentration by mass) over temperatures in the range of 23 °C to −35 °C. Electrical impedance spectroscopy, acoustic emission, and thermal measurements were made during cooling and heating to detect phase changes and resulting damage. The influence of the degree of saturation (DOS) and NaCl solution concentrations are examined. Three phase changes were detected: (1) eutectic phase change (∼−24 °C), (2) ice/water phase change (∼−4 °C to −4 °C), and (3) chemical phase change (∼−4.5 °C to −5.5 °C). While the resistivity is highly dependent on changes in temperature, a drastic increase in resistivity is observed during freezing. Additionally, a comparison of specimens above and below the critical DOS (i.e., the DOS required for damage to occur) shows that resistivity measurements may able to be used to quantify damage.

Abstract: The transport of fluid and ions in concrete mixtures is central to many aspects of concrete deterioration. As a result, transport properties are frequently measured as an indication of the durability that a concrete mixture may be expected to have. This paper is the second in a series investigating the performance of high volume fly ash (HVFA) mixtures with low water-to-cementitious ratios (w/cm) that are internally cured. While the first paper focused on strength and shrinkage, this paper presents the evaluation of the transport properties of these mixtures. Specifically, the paper presents results from: rapid chloride migration (RCM), rapid chloride penetration test (RCPT), apparent chloride diffusion coefficient, surface electrical resistivity, and water absorption. The test matrix consisted of mortar samples with two levels of class C fly ash replacement (40% and 60% by volume) with and without internal curing provided with pre-wetted lightweight fine aggregates (LWA). These mixtures are compared to plain ordinary portland cement (OPC) mortars. The results indicate that HVFA mixtures with and without internal curing provide benefits in terms of reduced transport coefficients compared to the OPC mixtures.

Abstract: Concrete is a unique composite material that is porous and highly heterogeneous. The durability of steel reinforced concrete in chloride environments is of great interest to design engineers, infrastructure owners and maintainers, and researchers. This review reports recent advances in the knowledge base relevant to the durability of steel reinforced concrete in chloride environments, including: the role of mineral admixtures in concrete durability, the methods of measuring the chloride ingress into concrete, the challenges in assessing concrete durability from its chloride diffusivity, and the service life modeling of reinforced concrete in chloride-laden environments. It concludes with a look to the future, including research needs to be addressed.

Abstract: The use of fly ash in concrete dates back to the late 20th century and its advantages and disadvantages had been widely researched. Despite the broad based research carried out across the globe in utilizing fly ash as a cement replacement material in concrete, the level of replacement is still limited to a maximum of 35% of cement by mass. In view of increasing the level of fly ash replacement in cement to minimize the carbon footprint, this work summarizes the following: firstly, the current state of fly ash applications in concrete by considering about 200 papers published since 1980 to till date. Secondly, the analysis of form-structure-property of fly ash reported in various literature and its correlation with strength and durability characteristics. Thirdly, the contradictions reported in literature regarding the performance of fly ash, particularly, in the context of shrinkage, high temperature curing, water demand etc. Overall, this review brings to light that, apart from chemical composition, the influence of other factors such as morphology, crystallinity, size etc. have major influence in altering the hydration mechanism which in turn bring changes in mechanical and durability properties of fly ash concrete. The critical examination of properties of fly ash provides insight for wider utilization of fly ash, facilitating a higher replacement of cement possibly upto 60% in a scientific way rather than by trial and error basis. Further, this review recommends for the classification of fly ash apart from the existing ASTM classification of fly ash as Class F and Class C. Furthermore, amendments in existing codes are recommended for high volume utilization of fly ash.

Abstract: In this review we discuss a wide range of alternative approaches to the reduction of CO 2 emissions associated with the manufacture of the binder phase in concrete. They are classified broadly as follows: (1) Use alternative fuels and/or alternative raw materials in the manufacture of Portland-based cements. (2) Replace Portland clinker with “low-carbon” supplementary cementitious materials (SCMs) in concrete. (3) Develop alternative low-carbon binders not based on Portland clinkers. The first approach mainly represents incremental improvements that can be achieved fairly easily and cheaply as long as suitable raw materials can be found. The second approach ranges from incremental improvements, if low levels of SCM substitution are used, all the way to major innovations for binders with very high Portland clinker replacement levels. The third approach is the most risky but also holds the greatest promise for truly significant CO 2 reductions if it can be implemented on a large scale.

Abstract: Fluid ingress is a primary factor that influences freeze-thaw damage in concrete. This paper discusses the influence of fluid ingress on freeze-thaw damage development. Specifically, this paper examines the influence of entrained air content on the rate of water absorption, the degree of saturation, and the relationship between the saturation level and freeze-thaw damage. The results indicate that whereas air content delays the time it takes for concrete to reach a critical degree of saturation it will not prevent the freeze-thaw damage from occurring. The results of the experiments show that when the degree of saturation exceeds 86–88%, freeze-thaw damage is inevitable with or without entrained air even with very few freeze-thaw cycles.

Abstract: Graphene oxide contains a range of reactive oxygen functional groups enables it as a suitable candidate for reaction in cementitious materials through physical functionalization. This paper aims to investigate the transport characteristics of graphene oxide reinforced cement composites that can be translated to concretes made with similar constituents. Transport characteristics determine the long term durability of concrete structures. Tests such as water sorptivity, chloride penetration and mercury intrusion porosimetry were performed to observe the effect of graphene oxide addition into cement matrix and its transport properties. Graphene oxide was dispersed into cement mortar to produce graphene oxide cement composite using additions of 0.01%, 0.03% and 0.06% by weight of cement. Experimental results indicate that incorporation of very low fraction of graphene oxide (0.01%) can effectively hinder the ingress of chloride ions. Additionally, the sorptivity are significantly enhanced by adding graphene oxide with a moderate fraction of 0.03%. It can be concluded that graphene oxide addition to cement matrix can effectively improve the cement matrix transport properties which subsequently improve its durability.