Raissa P. Ferron

Rheological method to evaluate structural buildup in self-consolidating concrete cement pastes

Much research has focused on determining the rheological properties of cementitious materials, but limited information can be found on the influence of thixotropy in affecting the flow properties of these materials. A protocol consisting of hysteresis loops and energy methods, was developed to quantify the degree of structural rebuilding in cement pastes. This protocol takes into account the stiffening due to thixotropic rebuilding and irreversible structural changes by focusing on the rate in which the cement paste is able to regain its internal structure after shearing. The protocol was used to evaluate the rebuilding potential of 23 cement paste mixtures of various binder type and fluidity level. Results show that structural build up can be controlled through selection of proper powder type, high-range water-reducing admixture, and water-to-binder ratio (w/b).

Experimental simulation of self-consolidating concrete formwork pressure

Developing a laboratory device to describe self-consolidating concretes (SCCs) formwork pressure behavior was this investigations aim. The cost and time needed for the same research to be conducted on real structures was reduced by the development of such an apparatus. Pressurizing a volume of material inside a cylinder and recording lateral pressure evolution allowed casting rate and mixture composition effects to be studied. There was simulation of two different casting rates and columns measuring 14 m (46 ft) in height. Four different water-binder (w/b) ratios and different binder compositions were used in mixture design. That less than hydrostatic formwork pressures were achievable was shown through results. Higher w/b and casting rates were associated with higher pressures. A casting rate of 7 m/hour (23 ft/hour) and a w/b of 0.32 was recorded for a formwork pressure reduction up to 50% of the hydrostatic value. That fly ash incorporation reduces SCC formwork pressure was also shown by data.

Cracking of Fiber-Reinforced Self-Compacting Concrete due to Restrained Shrinkage

Fiber-reinforced self-compacting concrete (FRSCC) is a new type of concrete mix that can mitigate two opposing weaknesses: poor workability in fiber-reinforced concrete and cracking resistance in plain SCC concrete. This study focused on early-age cracking of FRSCC due to restrained drying shrinkage, one of the most common causes of cracking. In order to investigate the effect of fiber on shrinkage cracking of FRSCC, ring shrinkage tests were performed for polypropylene and steel fiber-reinforced SCC. In addition, finite element analyses for those specimens were carried out considering drying shrinkage based on moisture diffusion, creep, cracking resistance of concrete, and the effect of fiber. The analysis results were verified via a comparison between the measured and calculated crack width. From the test and analysis results, the effectiveness of fiber with respect to reducing cracking was confirmed and some salient features on the shrinkage cracking of FRSCC were obtained.

Fresh concrete and its significance for sustainability

The push for sustainability initiatives in the construction field has been spearheaded by the green building movement. However, cement-based products and concrete are used in a variety of places, and not just buildings. While much effort on the sustainability of cement and concrete industry has been focused on cement production and the hardened state concrete – the fresh state performance and its role in sustainability has often been overlooked. Similar to hardened state concrete properties, understanding the microstructure of the fresh state concrete can provide the direction for tailoring the fresh state properties to improve the quality control, and thus the sustainability of concrete. This paper seeks to provide context for users of cement-based products to understand how the fresh state properties of concrete can be leveraged so that the quality control of concrete can be improved. Concepts such as flocculation, rheology, structural buildup, and formwork pressure will be discussed. The concepts discussed in this paper can be applied to various applications, from building to pavements to bridges to dams.

Cement Paste Reference Material (SRM2492) Shelf-Life Extension | NIST

Cement-based materials (e.g. cement paste, mortar and concrete) are complex rheological fluids that display time-dependent and shear-dependent rheological behavior. Over the years, various concrete rheometers have been proposed and made available commercially; however, there is no method to calibrate them. Furthermore, typical calibration fluids used in commercial rheometers are not well suited for the concrete rheometer calibration due to their high cost and they are Newtonian (i.e., not a complex fluid). Therefore, there was a clear need for a reference material specifically designed for concentrated, granular suspensions, such as cement paste, mortar and concrete; this need led to the development of a new series of reference materials for calibration of devices used in cement-based suspension rheological testing. The reference material to simulate cement paste, SRM 2492, was composed of a fine limestone powder in a corn syrup matrix. While the ranking of mixtures tested using these rheometers tend to match, the absolute values for the rheological properties of the mixtures evaluated with different rheometers are not well correlated [1, 2]. Additionally, due to microbial growth in the paste matrix, the shelf life of standard reference material 2492 was limited to 7 d. This paper presents the results of a study to analyze how to minimize microbial growth within the paste matrix. Various biocides that extend the shelf-life of the reference material were examined, with the most promising method being sodium propionate, a non-toxic chemical. Furthermore, recommendations to improve the storage of SRM are provided to extend the usable shelf life.

Calcined Shale as Low Cost Supplementary Cementitious Material

Despite the various benefits of using metakaolin as a supplementary cementitious material (SCM), the high price of metakaolin limits its use in concrete to premium applications. However there are other sedimentary minerals, such as calcined shale, that may be able to fill the need for low cost, abundant SCMs in concrete construction. The study presented here investigated a low cost calcined shale, sourced from a lightweight aggregate producer, and compared its performance as an SCM to that of a commercially available metakaolin. The effect of both SCMs on compressive strength, resistance to alkali silica reaction and mixture workability were evaluated. Results show that, other than early age compressive strength, the performance of calcined shale in cementitious mixtures is comparable to that of metakaolin. Differences in behavior of the SCMs are discussed in the context of their chemical and physical properties.