Abstract
In order to modify the porous interfacial transition zone (ITZ) microstructure of concrete more efficiently, a method of coating aggregate surfaces by using several nanoparticles was evaluated in this study. The compressive strength, chloride penetration of sound, and pre-loading samples were assessed in relation to the type of coating materials used (slag, nano-CaCO3, and nano-SiO2) and the designed coating thickness (5, 10, and 15 μm). The ITZ microstructure was quantitatively determined via Backscattered electron (BSE) image analysis. Results showed that the overall performance of concrete is highly dependent on the coating materials and the designed coating thickness. Increasing the coating thickness of slag and nano-SiO2 could improve the chloride penetration resistance but decrease the compressive strength. Using nano-CaCO3 to coat the aggregate leads to a significant reduction in the properties of the so-prepared concrete. Though coating inert fine particles around aggregate could disturb the initial particle packing and modify the ITZ, it is not able to improve the overall concrete properties. Coating aggregate could determine the ITZ microstructure, especially within the region that is around 30 μm away from aggregate surface.
Highlights
Concrete is by far the most common building materials because of its low cost, the abundance of raw materials required, and its adaptability and versatility in manufacturing various structural shapes and environments
The interfacial transition zone (ITZ) has normally been considered as the weakest region in concrete, and, exerts a ITZ has normally been considered as the weakest in concrete, exerts greater on the mechanical properties than can beregion expected from itsand, sizetherefore
The chloride migration coefficient increases with the designed nano-CaCO3 coating thickness
Summary
Concrete is by far the most common building materials because of its low cost, the abundance of raw materials required, and its adaptability and versatility in manufacturing various structural shapes and environments. Combining the information from the literature [5,8,9,10], the microstructure of the ITZ can be summarized as follows: (i) A duplex film of Ca(OH) topped by or occasionally intermixed with Calcium Silicate Hydroxide (CSH) located in the vicinity of the aggregate This film could transform to a dense layer, followed by a deposit of CSH in the form of fiber; (ii) the region enriched by large Ca(OH) crystals and ettringite (AFt) is located after the duplex layer. Another feature of the ITZ is that a relatively higher porosity could be observed due to the orientation growth of calcium hydroxide and ettringite crystals in an open space. The mechanical properties and the chloride penetration before and after pre-loading of the so-prepared specimens were evaluated in relation to the types and dosages of nanomaterials
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