ABSTRACT
Alkali-activation of agro-industrial wastes as alternative binder to Portland cement (PC) is receiving more consideration most especially in the developed nations due to the issue of green-house gas (CO2) emission from the production process of (PC) and the need to improve the fresh and hardened properties of agro-industrial waste-based mortar and concrete. This research focused on alkali-activated millet husk ash (MHA)-calcium carbide waste (CCW) binder-based mortar for appropriate characterization of the materials and evaluating the fresh / hardened properties of the mortar produced. MHA – an agricultural by-product and CCW – an industrial by-product was examined as possible materials to be combined as alternative to PC. Three combination proportions of MHA – CCW (40:60, 45:55 and 50:50) was determined from CaO and SiO2 content), activated with 5, 10, 15 and 20 molar concentrations of Sodium Hydroxide (NaOH) and mortar produced at 1:3 binder/sand (b/s) and 0.5 water/binder (W/B) examined for binding, strength development and water absorption at varied curing age (3, 7, 14, 28, and 56 days respectively) in accordance to BS EN 196-1: 2016. The chemical analysis of the supplementary cementitious materials via X-ray fluorescent (XRF) revealed MHA having 73.4 % silica (SiO2) content and the aggregation of the main oxides (SiO2 + Al2O + Fe2O3) gives 88.1 % which is above 70 % minimum limit stipulated in ASTM C618 (2015) standard while CCW primarily contain CaO (66.1 %). The fresh properties examination of the binder pastes results revealed 45-55 (MHA-CCW) at 15M NaOH molarity possessing similar fresh properties as the control (PC). The tested mortar samples exhibited increasing performance for both properties examined with increasing NaOH concentration up to 15M but decreased performance at 20M for all combination proportions. The 7- and 14-days strength for 45-55 MHA-CCW activated with 15M NaOH were 10.72 (67 %) and 15.96 N/mm2 (79 %) respectively of the PC-based sample at same age. The 28days strength for the 45-55 MHA- CCW, 15M NaOH sample showed higher strength gain (29 %) as against 23 % strength gain of the PC-based mortar. Further curing of the alkali-activated MHA-CCW mortar till 56days resulted in additional 24 % strength gain over the 28th day as compared to the 7 % increase of the control`. The trend is same for all the alkali-activated MHA-CCW mortar studied up to 15M NaOH concentrations. The 15M NaOH activation of 45-55 MHA-CCW is considered by this study as the indicated proportion for good strength. However, recommends the utilization of 45-55 MHA-CCW, 15M NaOH in 1:3 binder/sand at 0.5 W/C for masonry work and further studies into the examination of the morphology and nature of the hydration as well as the formed microstructure should be undertaken.
CHAPTER ONE
1.0 INTRODUCTION
1.1 Background to the Study
Mortar, binders and concrete are crucial substances for expeditious urbanization. Binder is known as one of the key components in the social, economic, financial and infrastructural advancement of human society of any nation. Cement is a significant component in all kinds of construction as binder; and in previous years the cement market has been filled by one item, Portland cement (PC) (Tsado et al., 2014). In numerous countries, PC is very costly and this has seriously restricted the construction of moderate housing (Didel et al., 2014). Thus, developing alternative binder to PC is a magnificent choice at much lower cost toward making critical contribution in making low-cost building materials available and thereby results to less expensive shelters (Abdullahi et al, 2013). Olawuyi et al. (2017) reported that PC based binder is one of the most significant materials used in construction across the globe and is manufactured through calcination of calcium carbonate (CaCO3) in an oven at elevated temperature above 900oC to liberate calcium oxide (CaO) as carbon dioxide (CO2) content of it was emitted to the atmosphere as shown in Equation (1.1) and thus added about 5 % of the globe CO2 (Nattapong et al., 2011; Rubenstein, 2012).
⇒ (1.1)
This development has made it necessary to look for alternative to PC as a way of making building materials less expensive and abate green-house gas (GHG) emission occurring from PC manufacturing processes. Over years, research bearings on alternative to PC concentrated mainly on incomplete replacement while report on complete cement replacement in mortar / concrete production with an activator to facilitate its setting time and strength advancement are limited in literature (Habeeb & Mahmud, 2010).
The major constituents of a clean PC are silica (SiO2), alumina (Al2O3) and ferric oxide (Fe2O3) with strength determinant being the SiO2 which joined with CaO in the addition of water at any given temperature (Neville, 2012; Mehta & Monteiro, 2014) as shown in Equation (1.2). This results in the formation of calcium silicate hydrate – CaO-SiO2-H2O (C
– S – H), the final result for strength improvement as cement hydration advances after
water contact.
+ SiO2 , + Al2O3 + Fe2O3 ⇒ CaO, SiO2 , Al2 O3 , Fe2O3 (1.2)
MHA is a decent wellspring of silica content (Jimoh et al., 2013) while CCW has been accounted to be of high calcium oxide-showed as CaO in the chemical formula (Olawuyi et al., 2017). These were joined together and activated with alkaline in this research at different proportions as calculated from the molar concentration of the MHA/CCW as accounted in Olonade & Bello (2017). As indicated by Yunusa (2015), CCW produce calcium hydroxide when completely mixed in water as appeared in Equation 1.3 As indicated by Yunusa (2015),
CaC2 + 2H2O C2C2 + Ca(OH)2 ( 1.3)
As reviewed by Mehta and Monteiro (2014), Pozzolanic responses in the similar way as that of Portland cement using Tri-Calcium-Silicate (C3S) in the presence of water (H) to liberate Calcium-Silicate-Hydrate (C-S-H) and Calcium Hydroxide (CH).
These (Portland- Pozzolan) cement responses are illustrated in equation (1.4) and (1.5) as follows:
C3S + H C – S – H + CH (1.4)
Pozzolan + CH + H C-S-H (1.5)
Where C = CaO, S = SiO2 and H = (OH) –
The reaction in Equation (1.4) is considered to be quick and lime delivering while the response in Equation (1.5) is somewhat moderate or idle, contingent upon the properties of the pozzolanic material and doesn’t require nearness of PC (Auta et al., 2015 and Jimoh et al., 2013) yet a functioning wellspring of CaO, hence the thought for preference source of CaO to upgrade pozzolanic response with an agricultural waste ash (MHA) as SiO2 source is the focal point of the current investigation. Likewise, the utilization of alkali-activation can definitely improve the pace of the response and hence improve its workability (Ka’ase et al., 2018).
Alkali activation as clarified by Martinez & Palomo (2001) is the chemical procedure where indistinct structure is changed into a skeletal structure that displays cementitious properties. The material containing responsive SiO2 or Al2O3 can be enacted as appeared in condition (1.6) and (1.7).
NaOH + SiO2 N-S-H (Gel) as in geopolymer (1.6)
NaOH + Al3 O2 N-S-H (Gel) as in geopolymer (1.7)
Where N-S-H (Gel) is Sodium-Silicate-Hydrate gel.
Early strength development is a basic measure in construction industry since it decides the speed of construction. In this way, low early strength advancement is a deterrent in advancing Pozzolan utilization as PC substitution. In order to avoid the less early strength advancement and high setting occasions in pozzolanic materials, methods like alkali- activation have been recommended by (Kwabena, 2012).
Bakharev (2006) disclosed that concrete manufactured with the aid of alkali-activated fly ash with NaOH had a two-day development strength of 10 N/mm2 meanwhile at 28-days strength development was 60 N/mm2. Moreover, He also makes fly ash more active in reaction by adding Sodium Silicate (Na2SiO2) to attain two-day strength development of 2 N/mm2 and a 28-day compressive strength of 45 N/mm2.
1.2 Statement of the research problem
The quest to improve the setting time and early age strength development of agricultural and industrial waste as revealed by Kisharet et al. (2013); Olawuyi, et al. (2017); Egwuda et al. (2018); Enejiyon et al. (2018) and Okwute (2018) has made it necessary to search for reasonable activators to improve the workability of these materials. But, in previous years, researchers had shone their searchlight on numerous researches on the quest for preference binder which focused mainly on the partial substitution of the PC in mortar or concrete due to the sensitization on the atmospheric change credited to a worldwide temperature alteration (Abdullahi, 2013).
According to Enejiyon et al. (2018), at 56 days of curing agricultural / industrial waste (RHA/CCW) based mortar and PC showed that the strength of RHA/CCW based mortar (9.52N/mm2 is three times of PC-based mortar (30.72N/mm2). Therefore, recommended for the utilization of set accelerator other than superplasticizer to improve strength gaining/fast track the setting time, early/later strength advancement of agricultural/industrial waste- based mortar to attain strength that is almosautat the same to that of PC based mortar. Also, Okwute (2018) reported that MHA/CCW based mortar compressive strength of 5.08N/mm2 and 8.38N/mm2 against that of PC (18.44N/mm2 and 22.25N/mm2 at 28days and 56days respectively. Therefore, suggested the use of set accelerator admixture to improve the early and later strength advancement of agricultural/ industrial waste-based mortar.
1.3 Aim and Objectives of the Study
This research is aimed at the development of alternative binder for mortar using alkali- activated millet husk ash (MHA) and calcium carbide waste (CCW) with a view to establishing the good performance level in strength and durability of mortar made from such binders.
The specific objectives are to:
i. Study the chemical and physical properties of the constituent materials (MHA, CCW and sand).
ii. Determine optimum mix proportions of MHA and CCW with NaOH-activation for mortar production.
iii. Evaluate the fresh and the early- age characteristics of the alkali-activated mortar.
iv. Investigate the hardened properties and the effect of alkali-activator (NaOH) on the strength properties (density, compressive strength and water absorption) of the various mix proportion of mortar.
1.4 Scope of the Study
This study focused mainly on experimental toward making a preference binder for mortar by utilizing NaOH to facilitate agro-industrial waste materials reaction (MHA– as SiO2 source and CCW – as CaO source) at different mix proportions (40:60, 45:55 and 50:50) respectively as determined from the molar concentration of the binder contents. Meanwhile, the molarities of NaOH used for activation of this agro-industrial waste vary from 0M to 20M at 5M step intervals. It involved appropriate characterization of the materials and determining the fresh and hardened properties of the binder pastes and mortar samples. Mortar cubes of 1:3 cement/sand (s/s) and 0.5 water/cement (w/c) showed by BS EN 196-1:2016 as control were examined in comparison with MHA-CCW based-mortar at different mix proportions. The tests conducted were chemical property (X-Ray Fluorescence – XRF); The fineness of the binders examined using 75 µm sieve, particle size distribution (PSD) and BET specific surface area for even distribution; Fresh properties (standard consistency, setting time, soundness); strength advancement and water assimilation of the hardened mortar. These mortar cubes prepared were tested for strength advancement and water assimilation at different curing ages (3, 7, 14, 28 and 56 days) with their densities evaluating accordingly.
1.5 Justification for the Study
The end result of this study offers well explained technical information on the alkali- activation of the preference binder with decent carbon foot print and continually making environment eco-friendly. The outcome of this study can be used in designing the mix proportion for specified compressive strengths and achieving a complete PC usage in mortar cubes production with decent workability data that affirmed the use of these environmental-friendly innovation on the large scale for word impact and maintaining eco- system friendly environment.
The uses of alkali-activated MHA-CCW binder will drastically diminish over dependent on PC usage reduce both agricultural and industrial waste disposals, diminish of hazard due to alkaline pollution and continually usage of materials with low CO2 emission (Jimoh et al., 2013; Abdulfatai et al., 2013; Bakharev, 2006).
The strive for developing alternative binder cannot be over emphasized in the face of the critical changing of economic realities, carbon blue print and the need for sustainable eco- friendly environment. The problem therefore is not only to look for preference cementitious materials but to resolve the chemically combined issues of these pozzolans with a view to establishing the early strength advancement achieved and the rate of water assimilation of mortar/concrete made from that kind of binders. Integrating alkali-activation on the agro- industrial waste usage results to early setting time and quick strength advancement of the mortar/concrete leads offers contribution towards improving knowledge in concrete technology and development of our nation, Nigeria. To justify the use of these, potentially more energy efficient technology on the large scale and to have global impact, it is necessary to develop adequate performance data that can bring changes to building codes and standard.
Nigeria’s drive for Agriculture with millet creation as one fundamental harvest and Niger State being a significant millet delivering State in Nigeria with tremendous measure of millet husk loaded at dump destinations as waste is the inspiration for this investigation (Jimoh et al., 2013; Auta et al., 2015; Anowai & Jones 2015. This investigation is an endeavour to investigate the use of alkali to activate MHA-CCW as an preference binder for mortar and concrete manufacture, towards the provision of less expensive housing, diminish over dependent on PC, reduction of indiscriminate waste disposal in both urban and rural area (Utsev & Taku, 2012; Abdulfatai et al., 2013) and furthermore help to diminish natural risk presented by CO2 gas outflow during PC manufacture (Abdul-Wahab et al., 2016; Olawuyi et al., 2017; Razi et al., 2016; Zhang et al., 2014). The use of the alkaline to activate on these materials in mortar manufacture will result in energy preservation with economic, ecology and technical merit.
This material content is developed to serve as a GUIDE for students to conduct academic research
PROPERTIES OF ALKALI-ACTIVATED MILLET HUSK ASH – CALCIUM CARBIDE WASTE BINDER BASED-MORTAR
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