OPTIMISATION OF CARBON DIOXIDE (CO2) SEQUESTRATION USING SANDCRETE-TALC COMPOSITE

ABSTRACT

Global interest on CO2  emission reduction has triggered alternative cement formulation using non-classical raw materials. This work presents a study on optimisation of CO2 uptake by sandcrete-talc composite material. The morphology, mineralogical and oxide composition of the materials were characterized using Scanning Electron Microscopy (SEM), X-ray Diffractormeter (XRD) and X-ray fluorescence (XRF).The result obtained from XRF indicate that sand consist 50.213% SiO2.and 16.001% Si with other diminish amount of oxide and metals, while mineral talc consist of 48.932% SiO2  and 24.86% MgO and cement contain 52.911% CaO, 15.122% Ca and 11.55% SiO2  with minute quantities of Alkalis and other metallic oxides. The mathematical model for the determination of CO2 concentration and compressive strength of sandcrete-talc composite was developed and optimized by the application of two-level four factorial design. The result showed that as curring age increases with increase in talc and sand components at constant cement component, the CO2 concentration and compressive strength also increases. The developed predicted model showed that the optimal concentration of CO2 and  compressive  strength  obtained  were 0.289mol/dm3   and  3.506N/mm2   respectively after 28 day curing at an ambient condition.

CHAPTER ONE

1.0    INTRODUCTION

1.1    Background of the Study

It is a well-known fact that carbon dioxide plays an important role in the natural greenhouse warming of the Earth‟s atmosphere. The idea of climate warming related to CO2  increases, as propounded by Arrhenius among others in the late nineteenth century. In the 1930s and 1940s Guy Stewart Calendar at Imperial College (London) revived the warming theory and by the 1970s it was generally accepted that global surface temperatures would increase as CO2 concentrations increased(Zhong and Haigh, 2013). It was on this note that World leaders gathered in Kyoto, Japan, in December 1997 to consider a world treaty restricting emissions of „„greenhouse gases,‟‟ chiefly among them is carbon dioxide (CO2), that are thought to cause „„global warming‟‟,  severe increases in Earth‟s atmospheric and surface temperatures, with disastrous environmental consequences; this is however evident in the melting of ice caps, increased sea level rise and extreme weather conditions (Robinson et al., 1998). To be sure, CO2  levels have increased substantially since the Industrial Revolution, and are expected to continue doing so. Greenhouse gases cause plant life, and the animal life that depends upon it, to survive (Zhong and Haigh, 2013).

Currently one of the most pressing and globally recognised challenges is how to mitigate the effects of global environmental change brought about by increasing emissions of greenhouse gases, especially CO2 (Woodward et al., 2009).  A number of strategies have been proposed to deal with this problem. The most obvious way in which CO2 emissions can be reduced is by switching from burning fossil fuels to using non-fossil-fuel sources of energy such as nuclear energy, wave and wind power, and geothermal sources.

In response, a variety of schemes have been proposed to either draw-down the amount of CO2   in  the  atmosphere  or  mitigate  the  effects  of  global  warming  through  energy efficiency, alternative energy sources, energy conservation as well as carbon capture and sequestration. Hyseni (2017), stated that carbon sequestration strategies can be a clear path  in  mitigating  climate  change  as  well  as  neutralizing  the  excess  CO2   in  the atmosphere emitted through anthropogenic sources. There are several other mitigation strategies for CO2  that have been studied and are currently being used in various pilot projects to further increase the incentive to study this field.

Different methodologies and technologies have been developed for the sequestration of atmospheric carbon dioxide (Sunho et al., 2009). However CO2 capture and sequestration using sandcrete blend is probably the best short to long term solution for the reduction of atmospheric acidic emission in developing nations. The effects of admixture on sandcrete carbonation have not been highlighted by most researchers. Significant knowledge gap exits. This work presents a study on the optimization and analysis of CO2  sequestration using 2-factorial design.

The rapid growth in any country‟s economy and population requires additional physical infrastructures to accommodate additional various component of the Gross National Product. These physical infrastructures include residential and commercial buildings, agricultural and health facilities, on the other hand it requires the integration of engineering, project, and production management techniques. A Sandcrete block is an important material in building construction. It is widely used in Nigeria, Ghana, and other African countries as load bearing and non-load bearing walling units. British Standard 6073: 1981 Part 1 defines a block as a masonry unit of larger size in all dimensions than specified for bricks but no dimension should  exceed  650mm  nor  should  the height  exceed  either its  length  or  six  times  its thickness. The quality of sandcrete blocks is influenced by so many factors such as the quality of constituent materials, the process adopted in manufacture, duration of curing, forms and sizes of blocks.

Ngally et al. (2014) reported that talc is an hydrated magnesium silicate with chemical formula Mg3Si4O10(OH)2. Talc is hydrophobic material that easily blends and disappears within organic media including polymer. It is widely used in reinforcing filler in several industrial products such as, papers, paints, rubbers, polymers, ceramics and refractory materials. The composition of talc make it potential raw material in cement formulation, since magnesium can interact with phosphate to yield cementitious materials as in phosphate magnesia cement.  They can be roughly divided into two deposits types, Talc- carbonate (dominantly talc with variable amount of chlorite, dolomite and or magnesite), and Talc-chlorite (dominantly talc with chlorite).

One of the key durability indicators of sandcrete is the degree of carbonation. Understanding sandcrete micro-structure as it affects durability is the hallmark for most sandcrete researchers (Odigure, 2002). The degree of porosity, pore type and size, pore connectivity and their distributions coupled with mineral crystal sizes and arrangement in the solid matrix significantly affect physicochemical properties of cement-based materials (Naik and Kumar, 2010).

Rostami  et  al.  (2012)  studied  micro-  structure  of  cement  paste  subject  to  early age carbonation curing with aim of understanding the mechanism of concrete carbonation through micro-structure development. They found that early carbonation curing could accelerate the strength gain and increases durability of concrete. Research has shown that the three polymorphs (Calcite, Aragonite or Vaterite) of calcium carbonate could be formed  during  carbonation  as  CO2   ingress  into  the  concrete.  The  micro-structure  of calcite formed during carbonation is characterized by small closely crammed crystals of a circular shape with particle size of less than 3µm (Fermandez et al., 2004).

In  view  of  the  above  background,  this  research  studies  the  uptake  of  CO2    and performance  characterization  of  sandcrete-talc  composite  at  early age  of  carbonation curing, as it is evidence that talc is a raw material for the formation of the cementitious material by increasing binder phase formation held in the matrix and reduction of pores will  be probably observed.  However, this  study  demonstrated  how CO2   capture and sequestration using sandcrete-talc composite can be employed as a short to long term solution for the reduction of atmospheric emissions.

1.2    Statement of the Research Problem

The environment is under increasing threat from global carbon dioxide (CO2) emissions deriving from cement industry and human sources. Statistics have shown that Cement manufacturing industries are among the largest industries that emit CO2  to atmosphere, for every 1 ton of cement produced, 1.25 tons of CO2  is released to the atmosphere (IPCC, 2015). Rising atmospheric CO2 is also increasing the absorption of CO2 by seawater, causing the ocean to become more acidic, with potentially disruptive effects on marine plankton and coral reefs. Technically and economically feasible strategies are needed to mitigate the consequences of increased atmospheric CO2. This project seeks to find way of mitigating global warming using talc-cement composite as CO2 sequestration materials, thereby saving energy and creating an environmentally friendly condition.

1.3    Aim and Objectives of the study

This research work optimised carbon dioxide (CO2) uptake by Sandcrete-Talc composite at ambient conditions.

This aim was achieved through the following objectives:

i.      Characterization of the Sandcrete-Talc composite produced at ambient conditions using XRD, XRF and SEM.

ii.      Evaluation of the effect of carbonation on the compressive strength after 28 days.

iii.     Evaluating  the  optimal  process  condition  that  maximizes  CO2    uptake  and

compressive strength.

1.4    Justification of the Study

Increased burning of fossil fuels, deforestation, land degradation and various industry practices have resulted in high atmospheric CO2 levels creating global concern because of its implications towards climate change. These sources have increased global emissions of CO2 by 48% more than two decades ago thus accelerating the greenhouse gas effect and increasing the overall temperature of the planet by 0.8oC in 2013. Recently, global leaders committed to keep the overall temperature rise of the planet to under 2oC at the 21st Conference of Paris (COP21) in Paris promising to mitigate climate change by moving toward a carbon free future (Hyseni, 2017).

Researchers in building sector have indicated that between 50 to 60% of the total construction input goes into building materials especially cement. Also, the construction industry has witnessed a higher level of criticism and controversies over the issues of building, the main problem being the issue of using substandard building materials and construction process or methods. It is necessary to enhance the cement quality and to find new cementitious raw material to overcome the global warming challenge due to the production of the largely used Portland cement. This research area arouses interests, which  focuses  on  the  reduction  of  the  CO2   emission  and  for  alternative  cement formulation  using  non-classical  raw  materials.  Indeed,  the  Portland  cements  are considered to be a cause of the global warming increase due to the large amount of CO2 that is produced by the related industries. Another reason to seek for alternative cement formulation is the related energy cost for the production of hydraulic cements. In addition, the need of cement products to be used in humid or acidic environments has aroused interest in studies that focused on the development of cements with low setting time. This research will assist, in solving the problems resulting from release of green-house gases (global warming), when talc is used to substitute cement partially at different percentage of  replacement.  Cement  can  be  made  cheaper,  and  cement  raw  materials  may  be preserved. Hence the outcome of this would attempt to optimize the use of sandcrete buildings as an infrastructure for CO2 sequestration in Nigeria.

This research will assist, in solving the problems resulting from the release of green-house gases (global warming), when talc is used to substitute sand partially at different percentage of replacement.

1.5    Scope of the Study

The scope of this study was limited to the evaluation and optimisation of the process parameters affecting the uptake of CO2  by sandcrete-talc composite and it effect on compressive strength.

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