Student Projects – Spring 2019

Comparison of the effect of aluminum to decrease the dissolution kinetics of quartz and cristobalite at high pH

Responsible: Mahsa Bagheri, mahsa.bagheri@epfl.ch

Alkali-silica reaction (ASR), as a worldwide durability concern, causes cracks and damage in concrete structures, creating remarkable costs to repair or to reconstruct. ASR is a long-term chemical reaction between amorphous silica (from reactive aggregates) and alkalis (mainly from pore solution of cement paste), producing ASR products, which form an expansive gel in the presence of water.

Addition of supplementary cementitious materials (SCMs) to portland cement (PC) has been introduced to reduce or even stop expansion of ASR. Especially, alumina rich SCMs such as fly ash have been indicated to be more efficient in avoiding ASR. Chappex and Scrivener in 2012 showed the decrease in the rate of silica dissolution due to adsorption of aluminum on the reactive silica surface.

The main goal of the present project is to compare how aluminum is effective to decrease the dissolution kinetics of quartz and cristobalite at high pH. Inductively Coupled Plasma/Optical Emission Spectrometry (ICP-OES) will be used to determine the ion concentrations.

Influence of process variables on strength and microstructure development in limestone calcined clay based light weight blocks

Responsible : G.V.P.Bhagath Singh, bhagath.gangapatnam@epfl.ch

The development of sustainable construction and building materials with reduced environmental footprint in both manufacturing and operational phases of the material lifecycle is attracting increased interest in the housing and construction industry worldwide. Recent innovations have led to the development of light weight concrete, which combines the performance benefits and operational energy savings achievable through the use of lightweight blocks. The work outlined in this proposal involves developing a fundamental understanding of production of stable calcined clay based light weight blocks for various construction applications. The results of this investigation will form the basis for identifying different process variables such as alumina powder dosage and fineness on aeration of block. Finally, role of initial curing temperature on aeration, density and strength of the blocks will be evaluated.

The link between the microstructure and strength will be established. Different analytical techniques will be used to determine the phases and reaction path ways in the system. X-ray diffraction will be used to identify and quantify the different phases. Porosity will be evaluated using mercury intrusion porosimetry and scanning electron microscopy will be used to determine the morphology of the product.

Effect of Metakaolin in binders based on Calcium Aluminate Cement, Calcium Sulfate and Ordinary Portland Cement

Responsible: Sarra El Housseini, sarra.elhousseini@epfl.ch

Blends composed of Calcium Aluminate Cement (CAC) in combination with calcium sulfate (C$Hx) and Ordinary Portland Cement (OPC) are widely used in building chemistry application where fast setting, rapid drying and shrinkage compensation are required. In order to reduce the CO2 footprint, Supplementary Cementitious Materials (SCMs) such as Metakaolin are used to substitute part of the OPC. Moreover, the use of Metakaolin can improve concrete properties depending on a certain substitution rate and powder fineness.

This project aims to investigate chemical and mechanical aspects of the use of different calcium aluminate cements and the impact of Metakaolin in these systems. The effect of Metakaolin on solution composition and kinetics will be studied using pH, conductivity and ions concentrations measurements. The changes in the solid phase will be investigated using XRD, TGA,SEM-EDS.

Effect of zinc on C3A hydration

Responsible: Andrea Teixeira, andrea.teixeirapita@epfl.ch

Concrete is the most used material in the world thanks to its extraordinary combination of mechanical and durability properties, availability and cost. Concrete production is expected to double in the next 30 years but its production accounts for 7% of man-made CO2 emissions. Because of its CO2emission, industrial wastes are investigated as potential reactive substitutes for raw material in cement manufacture. However, substitution may limit the cement reactivity and downturn its early age strength.

To solve this problem, cement reactivity can be promoted by the incorporation of minor elements such as Zinc (Zn). Zn has been demonstrated to enhance cement hydration while having a low toxicity and being relatively abundant. Although there are studies on this subject, there is no concrete evidence of the mechanism by which Zn influence the cement hydration. For this reason, the effect of this element in the major phases of cement need to be investigated.

The aim of this project is to study the effect of Zn on C3A hydration. The synthesis and characterization of C3A systems with amount of 0, 1, 3, 5% of Zn will be studied. Calorimetry, X-ray diffraction (XRD) and SEM-EDX will help to characterize the reaction rate, phase assemblage and microstructure evolutions. These techniques are most widespread in academia and industry and will surely be useful to the student later on in her/his education or career.

Effect of set-controlling admixtures on cement hydration kinetics and microstructure development

Responsible: Yu Yan, yu.yan@epfl.ch

To optimize the applicability of cementitious materials in various conditions, set-controlling admixtures are usually added to adjust the setting time and workability. Another thorny problem caused by the violent silicate reaction during the first day, which is named as thermal cracking can also be partly controlled by adding retarders, a specific set of set-controlling admixtures which delay the setting time of cementitious materials. Although much used, the mechanism of retarding and more fundamentally the rate control mechanism of cement hydration are still full of controversy.

The goal of this project is thus to study the effect of typical retarders (sucrose, dextrin) and synthesis C-S-H nuclei as an accelerator on cement hydration by quantifying the nucleation and growth of C-S-H, the main and most important hydration product. Besides, a novel starch-based admixture which can lower the main hydration peak and shed new light on solving the thermal cracking problem will also be studied.Furthermore,this study will enable the input of these quantitative results in cement hydration model such as the “Needle model” for instance. These models can then run virtual experiments to predict the heat release of cement hydration and contributes to the understanding of cement hydration and interaction with set-controlling admixtures.

The student will work with isothermal calorimetry and high-resolution scanning electron microscope.She or he will on the fly learn to build a design of experiment, a very useful technique for practically any experimental work in the industry or academia.

Physical sulfate attack in partially immersed conditions

 Responsible: Qiao Wang, qiao.wang@epfl.ch

Sulfate attack occurs when concrete structures are exposed to sulfate containing soil, ground water or seawater. People differentiate two types of sulfate attack, so-called physical and chemical sulfate attack.

Considerable research effort in laboratories is given to chemical attack, but in the field most damage seems to be associated with physical attack.  The problem is this is difficult to study physical in the lab as it is difficult to reproduce the conditions of partial immersion in which it occurs. We have done some preliminary tests to see what will happen using our special “set-up”. If you are interested in this project, please continue your reading.

In order to mimic the field condition, we can choose the RH, solution concentration and w/b ratio close to ambient. After different times of exposure, we can test what we can get from these samples. The possible testing approaches consist of scanning electron microscopy, X-ray diffraction and mercury intrusion porosimetry.  Such techniques can give the morphology properties as well as the chemical analysis of the interest area in cement or mortar sample. In the project we will investigate which of these techniques gives us useful information about physical sulfate attack.

Development of a low-carbon cement formulation targeted for the industrial production of roof tiles

Responsible: Franco Zunino, franco.zunino@epfl.ch

Supplementary cementitious materials are probably the most widely adopted and technically feasible method to reduce the carbon footprint of cement industry. However, the amounts produced of many of these materials is imbalanced with the actual cement demand. Calcined clays, obtained after calcination of the raw ground clays, can be sourced in large quantities from natural reservoirs widely distributed worldwide.

This project will involve the student with a real problem from the industry, related to the application of LC3based cements to the manufacture of roof tiles. A specific set of target properties such as setting time, flowability and compressive strength will be defined, and an LC3formulation meeting these criteria will be designed accordingly. After the goal formulation is achieved, a trial production of roof tiles will be conducted in collaboration with an industrial partner.

During the project, the student will be exposed to different preparation and characterization techniques such as setting time measurements, flow table, compressive strength and microstructural characterization of cementitious materials. In addition, the student will have the opportunity to get involved in a realistic research and development scenario, interacting with other scientists in the laboratory and also with the industrial partner of the project.

Investigating natural chloride diffusion in alternative cementitious systems

Responsible : William Wilson, william.wilson@epfl.ch

Chloride-induced corrosion represents the most important threat to reinforced concrete structures exposed to de-icing salts or marine environments. Modern concrete incorporating supplementary cementitious materials (SCMs) can now be designed to prevent the chloride ions to reach the reinforcing bars before several decades. Nevertheless, the fundamental understanding of the different mechanisms responsible for chloride penetration still require further research to accurately model the service life of concrete exposed to chlorides.

In this semester project, the mission of the student will be to investigate the chloride diffusion capacity of hydrated cement systems and to establish a link with the multi-scale porosity. A series of alternative blended-cement systems will be investigated, with varying water-to-binder ratios and incorporating novel SCMs, such limestone calcined clay cements (LC3). More precisely, the student will work in collaboration with our research team using advanced experimental methods such as mercury intrusion porosimetry, a novel steady-state non-accelerated chloride diffusion setup, and micro X-ray fluorescence (to determine chloride profiles in bulk samples previously immersed for several months in chloride solutions). Ultimately, the aim will be to improve the prediction of the long-term resistance to chloride-induced corrosion of real concrete structures, using the collected experimental data as input for chloride transport modelling.

Effect of heterogeneous surfaces on the nucleation and growth of Calcium Silicate Hydrate (C-S-H) in sustainable and ecofriendly cements

Responsible : Paul Bowen, paul.bowen@epfl.chmaya.harris@epfl.ch, andrea.teixeirapita@epfl.ch

Concrete is extensively used in the construction industry including buildings, bridges, dams, tunnels, and even roads. It is traditionally made by mixing cement, water, and aggregate. Concrete production has a significant carbon footprint due to the huge quantities used and this is expected to double in the next 30 years. The replacement of clinker by supplementary cementitious materials (e.g. slag, fly ash, clay, silica –fume, limestone) is a promising strategy to reduce the carbon footprint of cementitious materials [1, 2]. This, however, can modify the hydration and reaction kinetics including the setting and strength of cement and concrete.

In Portland cement, the anhydrous phases reacts with water to form calcium silicate hydrate (C-S-H), calcium hydroxide (CH), ettringite, calcium monosulphoaluminate or calcium monocarboaluminate. C-S-H is the major hydration product and the main binding phase in Portland cement. C-S-H precipitates from the ions produced in the pore solution produced by the dissolution of the anhydrous phases [3,4]. Also, nuclei are generally observed on cement grains rather than in the solution during cement hydration.

To better understand C-S-H nucleation and growth, heterogeneous particles (e.g. synthetic C-S-H, quartz,and limestone) can be introduced in the cementitious system. Quartz is a non-reactive component but is known to nucleate C-S-H. Furthermore, limestone acts as heterogeneous substrate and gives a higher density of C-S-H on the surface when compared with quartz [5]. C-S-H itself has been long known to influence hydration kinetics [6], we will synthesize or used synthetic C-S-H particles produced at LMC [7]. During this project, we will evaluate the approach for better understanding of hydration kinetics in standard ordinary Portland cement (OPC) systems and eco-friendly systems such as those using calcined clays.

Objective: The aim of this project is to see how heterogeneous particles (e.g. C-S-H, quartz and limestone) introduced into a hydrating cement effect the hydration kinetics. The concentration of the heterogeneous substrate will be varied to help understand the effects on cement hydration and followed by Isothermal calorimetry. The hydrated products will be characterized by FTIR, XRD (LMC, EPFL) and TGA. The morphology and microstructure of the hydration products can be investigated by SEM and TEM (CIME or LMC, EPFL). If time allows strength measurements after 1, 7 and 28 days will be made.