Semester

Fall

Date of Graduation

2023

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Civil and Environmental Engineering

Committee Chair

Roger H.L. Chen

Committee Member

Fei Dai

Committee Member

P.V. Vijay

Committee Member

Kakan Dey

Committee Member

Hailin Li

Abstract

Alternative supplemental cementitious materials (SCMs) are increasingly utilized in novel ways to reduce the carbon footprint of the construction industry. Volcanic ash (VA) is an abundant natural resource in many regions of the world. It is used as an alternative SCM for partial Portland cement (PC) replacement, but its low reactivity limits its applications to 10-25 wt.%. Another factor for restriction of high volume (>50%) VA (HVVA) PC replacement in concrete is due to insufficient amounts of Ca(OH)2 produced during PC hydration. These limitations are circumvented by modifying the reactivity of VA and by increasing the source of Ca(OH)2 in the system. This can be achieved by: (1) incorporating individual reactive components, such as CaO, SiO2, and Al2O3, into the mix design; (2) activating the reactivity of VA through physical, chemical and thermal processes; (3) introducing amorphous materials (AMs) that contain high reactive components in their composition to form modified-VA (MVA) and take advantage of their synergistic effects; and (4) employing an additional source of Ca(OH)2 to enable a complete reaction of HVVA. To better utilize HVVA in concrete mixtures, a dependable method to enhance the reactivity efficiency is needed. In this study, a methodology to modify the reactivity of VA was developed and used to increase its performance. An analytical tool to link integrated reaction models and PC paste mortar performance was also developed.

Ca(OH)2-reactivity test (CRT) and ASTM C311/C618 reactivity tests are typically used as standard baselines to quantify the reactivity of VAs. This modified these reactivity tests to be reliable for evaluation of VA/MVA. The mechanical and thermal properties of environmentally friendly mix designs containing VA/MVA were experimentally measured. Materials with high amorphous content (>90 wt.%), such as slag (SL), silica fume (SF), and metakaolin (MK), were used to form MVA. A classification that can identify the level of reactivity of VA/MVA was developed based on modified-CRT (MCRT). VA sourced from four different origins were evaluated in this study based on MCRT. Three of them were found to be reactive, while one was non-reactive. Modification of these VAs with AMs (MVA) resulted in higher reactivities. Binary (PC+VA) and ternary (PC+MVA) mortars were developed at 50 wt.% PC replacement based on modified-ASTM C311/C618 reactivity tests. Comprehensive studies on heat evolution behavior and kinetics of binary and ternary pastes were conducted. Linear equations were formulated to estimate the strength of binary mortars as a function of the heat released by binary pastes. The modified reactivity tests show consistent results and has assessed reactivity more accurately than the standard tests found in literature. Results of ternary PC systems indicate that SL is the best candidate for modifying the reactivity of VA to form MVA due to lower consumption of Ca(OH)2, while systems with MK and SF suffer from Ca(OH)2 deficiency that hinder the development of strength.

The required amount of Ca(OH)2 for a complete reaction in each VA was calculated based on the VA’s reactivity index (RI). RI was determined based on modified ASTM C311/C618 reactivity test. Linear equations were formulated to estimate RI of VA, thereby facilitating the calculation of the required Ca(OH)2 in the system. The required amounts of Ca(OH)2 for different HVVAs range from 3-10 wt.% of the binder. This amount of Ca(OH)2 was dissolved in the mixing water and used to reproduce the ternary mortars and resulted in improved strength. A linear equation for estimating the amorphous content as a function of RI was formulated and used to distinguish the inert and the reactive portions in each VA. A linear equation was developed to calculate the mass of Ca(OH)2 consumed by each VA, which was then used in the integrated reactions models proposed in this research. Reaction kinetic parameters of VA/MVA systems were experimentally determined and used in integrated reactions models. A 0.5-m insulated cube used to measure adiabatic temperature rise (ATR) was developed. Multiple ATR estimation methods on a single mix design were compared to validate its applicability. Results indicate that all ATR estimation methods compare well with the measurements.

Binary (BIR) and ternary (TIR) integrated reaction models were proposed to simulate the binary and ternary hydration blends and predicts their various properties. The chemical reaction equations of VAs are used to estimate the mass of chemically bound water (mc) and gel water (mg), which have not been documented in the literature for VA. In addition, mc and mg for SL and SF were estimated based on their chemical reactions. The experimental heat of hydration was used to calibrate the BIR and TIR models, and thus determine their constant reaction coefficients. These models showed results that match well with the experimental measurements. Parametric analysis was performed using BIR and TIR models. Equation expressing gel/space ratio was modified based on the SiO2 chemical reaction of VA to predict the strength development. It was then further modified to consider the gel/space ratio of AMs. Equations to predict the compressive strength were proposed. The predicted and measured compressive strengths corresponded well. Insufficient Ca(OH)2 in concrete mixtures increases the risk of low strength. Therefore, the dissolved amount of Ca(OH)2 in the mixing water was considered in the models. The developed models show excellent benefits for evaluating the chemical, mechanical and thermal properties of VA/MVA-blended concrete. These models will enable engineers to predict concrete properties that can be used for modifying the reactivity in unique cement blends. They can also be used as a useful tool to take preventative actions to minimize the risk of low strength issues.

This work concluded that systems with 50 wt.% PC plus 35 wt.% VA and 15 wt.% SL with additionally dissolved Ca(OH)2 provide very promising results for alternative concrete mixture for use in industrial applications.

Embargo Reason

Publication Pending

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Available for download on Thursday, December 05, 2024

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