Requirements of design based on mechanical strength and leaching have been established ... to study heavy metal leaching. .... 1) NEN-7345:94 (tank test).
LEACHING STUDY OF ALKALI ACTIVATED MATERIALS FOR USE IN ROAD BUILDING Beleña-Pozo, I*, Ordoñez-Belloc, L.M., Aliques-Granero, J. Materials Research Technical Unit, AIDICO, Paterna (Spain)
Abstract Environmentally friendly cements have been designed by means of the alkali activation of soils taken from the levelled ground in road building (chiefly clays), and from various industrial wastes (Ground Granulated Blast Furnace Slag and Fly Ash). Requirements of design based on mechanical strength and leaching have been established taking into account their use as a binder for road building. Binary mixtures of Ground Granulated Blast Furnace Slag, Limestone Filler, Silica Filler and Soil Filler were alkali activated with a mixture of sodium carbonate, sodium hydroxide and sodium silicate. Alkali activated binders were compared with three types of Ordinary Portland Cements: CEM I-42.5R, CEM I-42.5R/SR and CEM II-B/L 32.5N. Mechanical compressive strength tests were carried out with the target of achieving similar performance as cement types II B/L 32.5N (> 16MPa (7 days) and 32.5-52.5 MPa (28 days)) or types I-42.5N (> 10MPa (2 days) and 42.562.5 MPa (28 days)). Leaching tests were carried out to guarantee the leaching of heavy metal concentrations in underground waters are within limits proposed by WHO (World Health Organization) or Spanish legislation. Two different tests were selected to study heavy metal leaching. A non-destructive test, which simulates the normal conditions of materials (samples, are in a monolithic stay) and a destructive one, which simulates extreme conditions of the material (samples are ground). These tests were carried out according to standards NEN-7345 34 (migration rate test) and NEN-7341 33 (diffusivity test). In all tested formulations, concentrations of leached heavy metals did not exceed the limits established by Spanish legislation and WHO conditions. The study concludes that more sustainable cements, based on industrial waste, soils and alkali solutions, can be employed in road building. They are technically efficient and environmentally friendly. Originality This work shows the feasibility of designing sustainable cements without clinker content by means of alkali-activation technology and by employing soils exposed during ground- levelling process in road building and various industrial wastes (Ground Granulated Blast Furnace Slag and Fly Ash) can also be used for concrete design and use in road building as base or sub-base. It has been proven by both, migration and availability leaching tests that these cements, even with heavy metal traces in their composition, are innocuous to the environment since toxic elements are encapsulated after hardening. Chief contributions The results of this work contribute to the development of sustainable cements for use in road building. It has been demonstrated that these materials are more sustainable than traditional cements, technically feasible and environmentally friendly. Compared to traditional cements, they reduce CO2 emissions (60-80%) and only industrial wastes such as aluminosilicates are required as a starting material. Alkali sources and pH are minimized (pH 13.3) adjusting mechanical strengths required for their use (Rc>35 MPa) and by means of Na2CO3 as sodium source to decrease embodied energy, cost and corrosive effect of fresh cement respect traditional formulations of alkali activated cements (around pH 14). Keywords: Leaching, migration, availability, durability, alkali activated materials, metakaolin, Ground granulated blast furnace slag, fly ash, clays, roads.
1. INTRODUCTION Since the Kyoto protocol and the evidence of a greenhouse effect in the atmosphere, there is an increasing demand for a reduction in CO2 emissions derived from different industrial sectors. The cement industry is responsible for around 5% of the total CO2 emissions to the atmosphere. More than 50 % comes from the limestone burning process, 40% from fuel combustion and 10% from transportation [COST C23, 2005]. In recent years, Alkali Activated Binders (AAM) have been proposed as part of the solution to this problem, due to the reduction of energy and CO2 emissions in processing. AAM consist of natural or synthetic aluminosilicates mixed with alkalis. In a short time, at low temperatures (
