Anti-adherent Molds Yield Hydraulic Concrete Samples Suitable for Assessments of Surface and Water Absorption

Erick Castellón,Ernesto Mora

doi:10.32732/jcec.2021.10.4.245

Abstract

To assess several quality parameters of hydraulic concrete, cubic samples of this material are commonly assembled in engineering laboratories using molds. It is ubiquitous the use of cubic metallic molds of volume 125 cm3; these molds require the application of demolding substances (such as oils) on their surfaces to avoid the adhesion of the final hardened concrete sample to the molds. Despite this common practice suitable for evaluating mechanical traits of the materials, the use of a demolding agent spoils the concrete samples for the assessment of surface and water absorption parameters. To overcome this difficulty, we propose a new anti-adherent cubic mold that requires no demolding agent. The construction of the new mold based on anti-adherent polytetrafluoroethene (PTFE, Teflon®) is described with its use. To assess the claimed advantages of the new anti-adherent molds in testing surface and water diffusion traits of concrete samples, experiments on water contact angles, rates of water absorption and drying were performed on concrete specimens obtained with the classic and the new PTFE molds. It was proved the advantage of the anti-adherent mold over common metallic molds. The use of an oil as demolding agent in the concrete samples assembled in metallic molds produced conspicuous differences of water contact angles and absorption in comparison to clean concrete samples produced with PTFE molds.

Highlights

Because of its versatility, general availability, moldability and hardening properties, hydraulic concrete has various applications, and has become one of the most used construction materials [1,2,3,4,5,6].Concrete materials are intrinsically heterogeneous Macroscopically, hardened concrete comprises three main components: concrete paste, fine aggregates and coarse aggregates; the concrete paste binds the fine and coarse aggregates [6,7,8,9,10]
The presence of demolding agents such as a light oil does not affect the mechanical traits of the concrete specimens assembled in metallic molds
It was verified that all the concrete samples prepared in metallic molds and in the proposed PTFE molds showed no significant differences of the compressive strength values

Summary

Introduction

General availability, moldability and hardening properties, hydraulic concrete has various applications, and has become one of the most used construction materials [1,2,3,4,5,6].Concrete materials are intrinsically heterogeneous Macroscopically, hardened concrete comprises three main components: concrete paste (hydraulic cement + water), fine aggregates and coarse aggregates; the concrete paste binds the fine and coarse aggregates [6,7,8,9,10]. The fine and coarse aggregates represent about 75 % of the volume of the hydraulic concrete Even though these aggregates can be viewed as dispersed inert materials in the concrete paste [8,9,10,11,12], they largely determine the properties of the fresh mixture and of the final hardened material [5,1315]. Concrete materials are considered composites formed of a hydrated crystalline matrix with fine and coarse aggregates embedded therein. Each component of concrete has a role in establishing the physical and chemical properties of the composite material These characteristics of concrete materials require rigorous quality assessments to warrant its suitability and durability [7,16,17]

Methods

Results

Conclusion