The Development of Sustainable Internal Curing Agents Using Natural Hollow Fibres

The incorporation of superabsorbent materials as internal curing agents has demonstrated effectiveness in mitigating self-desiccation and early-age cracking in cement mixes characterized by low water-to-binder ratios (w/b). However, concerns related to sustainability, availability, and cost have emerged, primarily due to the petroleum-based nature of common superabsorbent polymers (SAP). This PhD research aims to investigate the use of locally available milkweed (MW) fibres, which possess a unique hollow structure, as internal curing agents for low-w/b Portland cement mixes. The study focused on examining the impact of different pre-treatment methods on the morphology, chemical composition, and hygroscopic characteristics of MW fibres in the initial phase. Two pre-treatment methods, namely hydrothermal treatment (HT), and hybrid treatment (HY), a combination of hydrothermal treatment with alkaline treatment, were explored. Findings from the first phase indicated that both HT and HY treatments effectively enhanced the water absorption capacity of MW fibres. However, water retention was influenced by the morphology of the fibres. The HT treatment preserved the hollow structure of the fibres, leading to improved water retention, whereas the HY treatment caused significant morphological changes, resulting in a noticeable reduction in water retention. In the second phase of the study, the impact of pre-treated MW fibres on the effective w/b of cement mixes was assessed through rheological measurements. In addition, the influence of MW fibres on the heat of hydration and hydration products was investigated. The introduction of MW fibres to Portland cement paste induced a shift in their effective w/b to lower values, attributed to the absorption action of MW fibres during the pre-saturation process. Furthermore, using 0.1% wt. pre-treated MW fibres resulted in a 17% improvement in the degree of hydration compared to the reference sample. This was accomplished by ensuring an adequate amount of free water for the initial reaction of cement hydration and entrained water in the lumen for subsequent internal curing. In the third phase, the study investigated the kinetics of water transport from MW fibres to cementitious paste systems, using Nuclear Magnetic Resonance (NMR) and Differential Scanning Calorimetry (DSC). The observations revealed that both the morphological features and the release of extractives such as lignin impact the desorption kinetics of MW fibres' entrained water within cementitious matrices. The HT-MW fibres, with their preserved hollow morphology and enhanced hydrophilicity, exhibited the most effective performance, showing the highest amount of available internal curing water in the transverse relaxation time (T2) measurements. In contrast, the absence of lignin in the HY-MW fibres allowed hydration products to migrate into their lumen. This led to the early consumption of the entrained water, a process further exacerbated by the holes and defects in the fibre walls. The shrinkage, mechanical strength, and microstructural development of cementitious mixes after incorporating pre-treated MW fibres were examined in the final phase. The internal curing role of the pre-treated MW fibres proved effective in reducing autogenous shrinkage, with significant reductions of up to 28% for 7 days compared to the plain samples. In addition, hydration products were observed to penetrate the lumen of the HY-MW fibres to a depth of up to 150 micrometres. This penetration exacerbated drying shrinkage by facilitating moisture transport to the unsaturated environment. Consequently, this phenomenon led to a higher chance of cracking and also lower flexural strength in HY-MW fibres compared to HT- and N-MW fibres. The comprehensive analysis and findings of this PhD research supported the feasibility of using MW fibres as sustainable internal curing agents to effectively reduce autogenous shrinkage after applying straightforward, cost-effective, and low-carbon footprint pre-treatment methods

Validation of Empirical and Semi-empirical Net Radiation Models versus Observed Data for Cold Semi-arid Climate Condition

Introduction: Solar Net Radiation (Rn) is one of the most important component which influences soil heat flux, evapotranspiration rate and hydrological cycle. This parameter (Rn) is measured based on the difference between downward and upward shortwave (SW) and longwave (LW) irradiances reaching the Earth’s surface. Field measurements of Rn are scarce, expensive and difficult due to the instrumental maintenance. As a result, in most research cases, Rn is estimated by the empirical, semi-empirical and physical radiation models. Almorox et al. (2008) suggested a net radiation model based on a linear regression model by using global solar radiation (Rs) and sunshine hours. Alados et al. (2003) evaluated the relation between Rn and Rs for Spain. They showed that the models based on shortwave radiation works perfect in estimating solar net radiation. In another work, Irmak et al. (2003) presented two empirical Rn models, which worked with the minimum numbers of weather parameters. They evaluated their models for humid, dry, inland and coastal regions of the United States. They concluded that both Rn models work better than FAO-56 Penman-Monteith model. Sabziparvar et al. (2016) estimated the daily Rn for four climate types in Iran. They examined various net radiation models namely: Wright, Basic Regression Model (BRM), Linacre, Berliand, Irmak, and Monteith. Their results highlighted that on regional averages, the linear BRM model has the superior performance in generating the most accurate daily ET0. They also showed that for 70% of the study sites, the linear Rn models can be reliable candidates instead of sophisticated nonlinear Rn models. Having considered the importance of Rn in determining crop water requirement, the aim of this study is to obtain the best performance Rn model for cold semi-arid climate of Hamedan. Materials and Methods: We employed hourly and daily weather data and Rn data, which were measured during December 2011 to June 2013 in climatology station of Bu-Ali Sina University. This experiment was performed for the cold semi-arid site of Hamedan (Iran). The study site (Hamedan) is a mountainous research station (1860 meters above sea-level) which is located at the eastern side of central Zagros Mountain Range. The net radiation fluxes were measured by four SW (300-2800 nm) and LW (4500-42000 nm).Hukseflux Thermal Sensors mounted on an automatic logger system. The logger reported four upward and downward solar components in every 8-minute intervals. In this study, total daily net radiation was estimated by 12 empirical and semi-empirical Rn models including: Basic Regression Models (BRM), Extended Regression Models (ERM), Linacre, Berliand, Wright and FAO-56 Penman-Monteith. The model performances were evaluated by R2, RMSE, MBE and MPE criteria and the best model was selected accordingly. Results and Discussion: In this research, the model calculations were done for seasonal and annual time scales. The results indicate that Basic Regression Model Rn(BRM-4) performs the best estimates in spring time. Further, for summer and autumn seasons, Rn (BRM-3) was superior for the cold semi-arid climate of Hamedan. Therefore, with the exception of winter, the BRM models performed the best estimates. Unlike the other seasons, for winter, Irmak presented the most accurate results. This is due to the fact that net radiation as estimates by Irmak Model is mainly dependent on daily maximum (Tmax) and minimum temperatures. For Irmak model, as the Tmax is increased, Rn will be reduced proportionally. For this reason, Irmak does not perform good estimates for warm months. In annual time scale, the Basic Regression Model of Rn (BRM-3) presented the most accurate estimates of net radiation. The study of Monteith and Szeicz (1961)and MirgaloyBayat (2011) also showed that Rn (BRM-3) model can generated the best Rn estimate in annual scale for mountain regions. Conclusion: Unlike the recommendation of FAO for using Penman-Monteith and Wright approaches in evapotranspiration models, it was found that the aforesaid Rn models are not suitable for cold semi-arid regions such as Hamedan. This result is in good agreement with the findings of Izoimon et al. (2000) and MirgaloyBayat (2011). In general, for cold climate condition of Hamedan, the Basic Regression Models are more reliable than the other Rn models. This study was performed based on 18-month field data and 12-Rn models. To achieve more accurate results, using a longer term experimental data and examining more Rn models are suggested as the future works. To achieve a regional Rn zoning, inclusion of satellite-based dataset is also recommended

Analysis of Daily Global Solar Radiation Data for Wuhan

In order to improve knowledge on solar resources, this paper analyses the models correlating daily global solar radiation with sunshine duration for Wuhan, China. Estimated values were compared with measured values in terms of statistical error tests such as mean percentage error (MPE), mean bias error (MBE), root mean square error (RMSE). The model performing best was selected. The global solar radiation estimated from the best model was compared with measured values. It was determined that the predicted values have good agreement with the measured values at high daily global solar radiation

Comparison between Measurements and Models For Daily Global Solar Radiation of Urumuqi

In this study, daily global solar radiation data at Urumuqi in 1995-2004 were investigated. Sunshine based models were used to estimate the global radiation. Estimated values were compared with measured values in terms of statistical error tests such as mean percentage error (MPE), mean bias error (MBE), root mean square error (RMSE). The model performing best was selected. The global solar radiation estimated from the best model was compared with measured values. It was determined that the predicted values have good agreement with the measured values at high daily global solar radiation

General Formula for Estimation of Monthly Mean Global Solar Radiation in Different Climates on the South and North Coasts of Iran

Using sunshine duration, cloud cover, relative humidity, average of maximum temperature, and ground albedo as the input of several radiation models, the monthly average daily solar radiation on horizontal surface in various coastal cities of the South (25.23∘ N) and the North (38.42∘ N) of Iran are estimated. Several radiation models are tested and further are revised by taking into consideration the effects of relative humidity, ground albedo, and Sun-Earth distance. Model validation is performed by using up to 13 years (1988–2000) of daily solar observations. Errors are calculated using MBE, MABE, MPE, and RMSE statistical criteria (see nomenclature) and further a general formula which estimates the global radiation in different climates of coastal regions is suggested. The proposed method shows a good agreement (less than 7% deviation) with the long-term pyranometric data. In comparison with other works done so far, the suggested method performs a higher degree of accuracy for those of two regions. The model results can be extended to other locations in coastal regions where solar data are not available

An investigation into the microstructural evolution and shrinkage control in internally cured mortars with milkweed fibres

This study presented a significant advancement in the use of Milkweed (MW) fibres as internal curing agents in low water-to-cement (w/c) cementitious materials. The research focused on how different pre-treated MW fibres, with different composition, can impact internal curing efficacy in reducing autogenous shrinkage of cement mortars. In addition, the hydration behaviour and microstructural development were revealed using a series of tests including setting time, compressive strength, flexural strength, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA/DTG). A key finding of this study is the remarkable reduction in autogenous shrinkage, with using 0.1 % wt. pre-treated MW fibres leading to up to 28 % reduction at 7 days, compared to plain mortars. Furthermore, internal curing effect resulted in narrowing the compressive strength gap between the reference mixes and those with pre-treated MW fibres in the later stages of hydration. It was also found that the removal of hemicellulose through hybrid treatment can reduce the delay in the final setting time of cement from 45 minutes to 18 minutes. Additionally, while the incorporation of N- and HT-treated MW fibres had negligible effects on drying shrinkage, the inclusion of HY-treated MW fibres led to a 15 % increase in drying shrinkage at 7 days. This difference in behaviour was attributed to the presence of lignin in N- and HT-treated fibres. Lignin was found to play a crucial role in influencing the drying shrinkage, microstructural development, and mechanical properties of MW fibre-incorporated cementitious mixes. Acting as a protective barrier, lignin shielded the MW fibres from cement infiltration into their lumina. Moreover, it served as both a physical and chemical barrier, reducing moisture transport through the capillary network during drying. In conclusion, this study demonstrated the potential of using pre-treated MW fibres as internal curing agents to effectively reduce autogenous shrinkage, with minimal compromise in terms of the compressive strength of cementitious composites