Influence of aggregate characteristics on concrete performance

Abstract

While the influence of paste properties on concrete performance has been extensively studied and in many cases reduced to quantitative relationships (e.g., Abram's law), that between aggregate characteristics and concrete performance has not been investigated in detail. Based on previous research that demonstrated significant strength differences for two similar concrete mixtures, one prepared with limestone aggregates and the other with siliceous gravel, a joint study between the National Institute of Standards and Technology (NIST) and the Federal Highway Administration (FHWA) was initiated to explore in detail the influence of aggregate source, mineralogy, and material properties on concrete performance. Eleven aggregates of differing mineralogy were identified and obtained both for bulk characterization and for incorporation into two concrete mixtures. The first concrete mixture was based on a 100 % ordinary Type I/II portland cement (OPC), while the second consisted of a ternary 60:30:10 volumetric blend of this cement with 30 % of a Class C fly ash and 10 % of a fine limestone powder. This latter sustainable mixture had exhibited exemplary performance in a previous study. Aggregates were characterized with respect to mechanical and thermomechanical properties, geometrical characteristics, and surface energies. For the prepared concretes, mechanical, thermomechanical, and electrical properties were measured at different ages out to 91 d and microstructural examinations were conducted to examine the interfaces between aggregates and cement paste. Concrete performance varied widely amongst the different aggregates, with the (range/average) ratio for 28-d compressive strength being 0.32 for the OPC concretes and 0.37 for those based on the ternary blend binder. With the exceptions of relating concrete modulus to aggregate modulus and concrete coefficient of thermal expansion (CTE) to aggregate CTE, weak correlations were generally obtained between a single aggregate characteristic and concrete performance properties. Models to predict 28-d compressive strength based on the aggregates' CTE (and aggregate absorption in the case of the ternary blend mixtures) provided predictions with a relative standard error (standard error/mean) of about 7 %. It is suggested that aggregate and binder characteristics control the bond between aggregates and paste. Then, for most properties, concrete performance is primarily controlled by the level of this bonding, a characteristic that was only assessed in an indirect manner in the present study. Research using non-linear ultrasonic measurements to better assess this bonding in specimens remaining from the present study is currently underway.

Influence of substrate moisture state and roughness on interface microstructure and bond strength: Slant shear vs. pull-off testing

“…At the FHWA laboratory, an ordinary portland cement, ASTM C150-16 Type I/II, with a manufacturer-reported Blaine fineness of 382 m 2 /kg and density of 3070 kg/m 3 , was used to prepare a concrete with exposed aggregates to serve as the existing substrate [14], with the fine aggregate (FA) being an ordinary river sand (apparent specific gravity of 2.59) and the coarse aggregate (CA) being a dolomitic limestone (apparent specific gravity of 2.85). Dolomitic limestone aggregates have been observed to provide good bonding to paste and high strengths (compressive, flexural, and splitting tensile) and elastic modulus in both ordinary portland cement and ternary blend (cement, fly ash, and fine limestone) concretes in a recent joint NIST/FHWA study of the influence of aggregate characteristics on concrete performance [28]. For the present study, the concrete mixture was developed with a water-to-cement ratio ( w/c ) of 0.35 by mass, cement:FA:CA ratio of 1:1.7:2.5 (by mass), a minimum slump of 76 mm (3 in.)…”

4D printing structures for extreme temperatures using metakaolin based geopolymers

“…In the past decade, the United States' production has grown from 67 million metric tons to 90 million (Lehne and Preston 2018). OPC composites in the form of mortar and concrete create structures such as sidewalks, foundations, floors, and columns, and the desired strengths for each application has been varied and optimized over time (Bentz et al 2017;Vu et al 2020). GP composites have been regarded highly in the literature due to high mechanical properties, namely compressive and flexural strength, and the relatively low-emission production of metakaolin is desirable in using GP composites as an alternative to concrete (Ramujee and PothaRaju 2017).…”

“…A low cement and aggregate ratio, such as a mixture with too much sand, also lowers the mechanical strength of concrete and results in a grainy texture that will be unable to bind together. The shape, size, and strength of the aggregates used are important, especially when making concrete with sand and coarse aggregates such as gravel (Bentz et al 2017;Vu et al 2020;Abdullahi 2012;The Engineering ToolBox 2009).…”

Numerical and Experimental Investigation of Wall Effect in Concrete

“…Table 2 reports the properties of each phase. Bulk and shear moduli are taken from [3]. The permeability of aggregates is very low compared to mortars permeability.…”

“…Altogether, these aspects lead to changes in the properties of a superficial layer, and these changes can be relevant to some applications of cement-based materials and concrete structures potentially affecting their performances [1], [2]. The skin of the concrete is in direct contact with aggressive agents such as chlorides and carbon dioxide [3]. If it has weaker properties than the bulk area of the material, this implies an increase in the risk of the appearance of pathologies or the acceleration of its appearance.…”