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August 2015 - present
Publications
Publications (64)
The goal of this study is to assess the effectiveness of a Problem-Based Learning (PBL) pedagogy that was implemented in two different concrete construction courses. Both courses are a part of an industry focused four-year undergraduate concrete degree program. One of the classes focused on concrete problems, diagnosis, and repair of existing concr...
A high-performance concrete rapid patching repair material needs to develop high early strength to satisfy traffic opening requirements, yet provides sufficient durability to sustain different environmental conditions and primary deterioration mechanisms for full-depth concrete repair. In this study, a set of experiments was conducted to evaluate t...
Fly ash-based geopolymer is an attractive supplemental cementitious material that has been receiving great attention from the community; however, its durability characteristics such as resistance to sulfate-related damage have not yet been fully examined. This study investigates the properties of fly ash-based geopolymer and its counterpart, Type V...
Recycling, being one of the strategies in minimizing waste, offers three benefits: it lessens the demand for new resources, reduces transportation and production energy costs, and beneficially reutilizes waste, which would otherwise be lost in landfill sites. While it is believed that recycled concrete aggregate (RCA) can be effectively incorporate...
In this study, the initiation and development of alkali–silica reaction (ASR) in concrete prisms containing reactive coarse (RCA) and reactive fine (RFA) aggregates were monitored over one year using linear and nonlinear resonance techniques. Although the linear resonance test could detect initiation and development of ASR damage in RCA specimens,...
The United States is by far the largest corn producer worldwide, with corn yields steadily increasing for the past decades. In many midwestern U.S. states such as Iowa, Illinois, and Nebraska, corn farmers currently grow more corn than consumers can utilize as human food or animal feed. To sustain the economic viability of corn farmers, it is criti...
Concrete is the most significant building material worldwide due to its excellent mechanical properties and durability. In this regard, recycling and reusing the demolished concrete as new construction materials can greatly contribute to achieving sustainable development. One of the most promising ways to reuse such waste concrete is to produce rec...
Nebraska has used reclaimed asphalt pavement (RAP) materials (in a range of 20-50%) over more than 10 years in pavement construction. Despite the immediate economic and environmental benefits it has been reported that incorporating RAP may reduce pavement durability and crack resistance. This study used NDOT's database to investigate the effect of...
Balanced mixture design is an alternative asphalt concrete design method that incorporates the performance of mixtures during the design. Balanced mixture design consists of performance test methods and performance criteria. Compared to the existing Superpave design method which mostly relies on volumetrics to design mixtures, balanced mixture desi...
Pavement rehabilitation practice involves milling an asphalt surface and placing a new layer. The incorporation of reclaimed asphalt pavement (RAP) mixtures brings cost savings and preserves the environment and natural resources. However, the use of recycled materials can compromise pavement performance, in particular, RAP can contribute to crackin...
Due to the relatively high cement content and low water-to-cement ratio (w/c) used, bridge deck concrete is prone to premature cracking. Internal curing has been found to greatly reduce the chance of premature cracking as well as concrete deterioration. This research project was intended to develop internally cured bridge deck concrete based on a l...
Ultra-high performance concrete (UHPC) is a new class of concrete that has superior mechanical, durability, and workability properties that far exceed those of conventional concrete. To achieve these properties, a specific mix design with a very dense internal structure, fiber reinforcement, and low water-to-binder ratio (w/b) is commonly used. The...
The main objective of this research project was to achieve a cement reduction on Nebraska slip-form pavement concrete through aggregate particle packing optimization. A literature review was conducted to examine different aggregate optimization tools, quality control tests, and historical data of Nebraska Department of Transportation (NDOT) pavemen...
Concrete pavements exhibiting severe distresses which require patching are commonly observed in the concrete pavement in Nebraska. Due to the requirements of opening pavement to traffic after placing the rapid patching materials, it is essential for that concrete to achieve high early strength. To ensure this, a high cement content and chloride-bas...
Many county-owned bridges in Nebraska need replacement due to their structural deficiency. Most of the bridges needing replacement are in the 40 to 60 ft range. This span range lacks a standard design that fits Nebraska county practices in terms of speed and simplicity of construction. The current systems being used are (a) Precast 1 by 2 ft planks...
Because of the requirements of opening pavement to traffic after placing repair concrete, it is essential for that concrete to achieve high early strength. To ensure this, a high cement content is generally used in Portland cement-based rapid-patching materials. Besides its associated high cost, high cement content tends to result in a less stable...
During the last decades, cellular lightweight concrete (CLC), or foamed concrete, has been experiencing greater interest in geotechnical, structural, and non-structural applications. The low density and high flowability makes it a favorable construction material in relation to handling, placing, and construction costs. However, the applications of...
In recent years, the use of Ultra-High Performance Concrete (UHPC) in bridge construction has been growing significantly. UHPC is considered an ideal material for bridge connections due to its excellent early-age mechanical properties, exceptional durability, and high workability. The objective of this paper is to evaluate the interface shear resis...
Alkali-activated fly ash (AAFA) is usually cured at elevated temperature, which limits its wide field applications. However, several studies have shown that properties of AAFA cured at ambient temperature can be significantly improved by incorporating different cementitious additives. This research investigated the impact of substituting a small po...
The quick accumulation of recycled organic components with the modern society development has caused serious environment issues, and the utilization of these recycled organic components in concrete production can effectively mitigate recycling pressure. Portland cement concrete mixes containing recycled organic components behave differently in both...
To successfully process concrete, it is necessary to predict and control its flow behavior. However, the workability of concrete is not completely measured or specified by current standard tests. Furthermore, it is only with a clear picture of cement hydration and setting that full prediction and control of concrete performance can be generalized....
Concrete is the corner stone of the construction industry and the second largest material being used after water. The growth of theconstruction industry and an increasing awareness of the environmental impact of human activity has accelerated thedevelopment of environment friendly solutions in concrete production and construction. Through the produ...
Self-consolidating concrete (SCC) is an innovative type of concrete that requires little to no mechanical vibration, and can be consolidated into formwork under its own weight. While the precast concrete industry has fully adopted SCC because of its tremendous benefits, the overall use of SCC in the concrete market, particularly in the ready-mixed...
In recent years, pervious concrete has become an emerging material for healthier ground water recharge and superior control of high stormwater runoff. This is facilitated by the high void content of the material. The void content percentage is an important design variable, as it correlates permeability as well as the strength of the material. There...
PURPOSES : This paper presents a description of the current issues facing road managers regarding the surface-type conversion of lowvolume roads for cost savings.
METHODS: The paper reviews previous works conducted toward this end, acknowledges gaps in the current research, and lays out what information is needed for further studies.
RESULTS : If t...
Although joint sawing has been widely used in concrete pavement to prevent uncontrolled cracking, optimum timing of joint sawing is critical to ensure appropriate crack control in designed joint locations. This paper presents a study of using concrete embedment strain gauges to monitor cracking at sawed joints by measuring the strain development at...
Fresh concrete can exhibit different rheological behavior when at rest than when flowing. This difference is due to thixotropy, which can have important consequences for formwork pressure, multi-lift casting, slip-form paving, pumping, and segregation resistance. This TechNote defines thixotropy and distinguishes it from other changes in rheologica...
This paper presents a case study of inspection and evaluation of a concrete bridge located in southeast Texas. A significant level of deterioration of concrete columns in the bridge has generated public concerns regarding its structure integrity. Many environment-related factors (including erosion, abrasion, wetting/drying, carbonation, freezing-th...
The critical element for sustainable growth in the construction industry is the development of alternative cements. A new technological process called geopolymerization provides an innovative solution, and the presence of aluminum and silicon oxides in fly ash has encouraged its use as a source material. Many previous investigations have involved c...
Two-lift concrete paving (2LCP) involves placing two layers of concrete (wet-on-wet) instead of a single homogeneous layer. The practice not only allows the use of local aggregates that might not be suitable for conventional pavement, but also provides opportunities for incorporating recycled materials and higher levels of supplemental cementitious...
In this study, hydration of mortars containing portland cement of three different finenesses and prepared at four different water-to-cement ratios (w/c) were investigated using isothermal calorimetry tests. Results showed that the hydration heat generated from cement with higher fineness was larger and faster compared to coarser cements in early ag...
Concrete recycling provides sustainability benefits in conservation of virgin aggregate resources, landfill reduction, energy savings, and reduced greenhouse gases emission. Effective and new uses of recycled concrete aggregate (RCA) in cement and concrete industry have attracted a lot of researchers’ attention from the perspective of environmental...
Thermal properties, such as coefficient of thermal expansion (CTE) and thermal conductivity, are important parameters in pavement design. Improper use of aggregates or pavements with different thermal properties might result in extensive stresses and potential cracking in concrete pavement, which could lead to durability issues. In order to better...
This paper presents the results of an experimental programme to investigate the effects of the concrete mix parameters on the mechanical properties of aerated lightweight aggregate concrete (ALAC). The compressive strength, modulus of elasticity, split tensile strength and Poisson ratio were investigated for 60 different concretes, with densities r...
A systematic study has been conducted to evaluate the ability of portland cement to sequester lead in concrete. Four different masonry materials (two types of concrete blocks and two types of clay bricks) that contained lead-based paint (LBP) were crushed and used as aggregate in concrete.
Properties such as gradation, absorption and lead toxicity...
This paper presents artificial neural network techniques for predicting the compressive strength of Aerated Lightweight Aggregate Concrete (ALAC) based on the effects of the concrete mix parameters. The compressive strength of sixty different concretes with densities ranging from 551 to 1948 kg/m3 was used and trained. The primary mix design variab...
This study was initiated to investigate the aging characteristics of binders due to the reaction with the crumb rubber. For this laboratory study, the crumb rubber modified (CRM) and control binders were aged using an oven aging method. Also, asphalt mixtures with CRM or control binders were made and subjected to short-term and long-term aging trea...
In the present study, concrete was considered as a two-phase material, consisting of coarse aggregate (CA) and mortar. Coarse aggregate properties were characterized by fineness, uncompacted void and friction angle. The combined effects of CA characteristics and mix design on the rheological properties of the corresponding concrete were investigate...
This research aims to evaluate the calorimetry tests for characterizing cement hydration properties and predicting temperature developments of the early-age Portland cement concrete pavement (PCCP). Analytical models are studied to simulate hydration properties, using the measured heat evolution data from both the isothermal and semi-adiabatic test...
Four lead-based paint (LBP) contaminated deconstructed masonry materials (two types of concrete blocks and two types of clay bricks) were crushed and used to replace all natural aggregate in conventional concrete. To reduce cost, the crushed materials were neither sieved nor re-graded. After their physical properties and lead-leaching ability were...
The present research was designed to study the mechanical properties of typical portland cement concrete (PCC) used in Iowa pavements. These properties are required as input values by the AASHTO Mechanistic-Empirical Pavement Design Guide (MEPDG). In this research, over 20,000 data were collected, compiled, and statistically analyzed. The typical i...
Degree of cement hydration can be characterized by hydration parameters including activation energy (Ea) and hydration curve parameters (ultimate hydration degree αu, hydration shape parameter β, and hydration time parameter τ). These parameters are affected by material compositions including chemical and mineral admixtures. In this study, isotherm...
Fiber reinforced aerated lightweight concrete (FALC) was developed to reduce concrete's density and to improve its fire resistance, thermal conductivity, and energy absorption. Compression tests were performed to determine basic properties of FALC. The primary independent variables were the types and volume fraction of fibers, and the amount of air...
The present research was designed to determine thermal properties, such as coefficient of thermal expansion (CTE) and thermal conductivity, of portland cement concrete (PCC) used in Iowa pavements. These properties are required as input values by the AASHTO Mechanistic-Empirical Pavement Design Guide (MEPDG). In this research, a literature survey w...
The effects of aggregate characteristics on the flow ability of mortar mixtures were investigated. Two types, five single-sized and three graded fine aggregate were considered. Uncompacted voids of the aggregates were measured. Flow properties of 166 mortar batches made with different aggregates, sand-to-cement ratios (s/c) and water-to-cement rati...
The present research is to explore a new approach to monitoring uniformity of concrete mixtures. A given concrete mix was subjected to three different mixing procedures. A moisture sensor was installed inside a pan mixer to monitor moisture content of the concrete mixtures during mixing. The concrete mixtures were considered as uniformly mixed when...
In this paper, operation, data interpretation, and validity of vibrating slope apparatus (VSA) tests for concrete flow property measurements were investigated. Results from standard slump tests and VSA tests of 14 different concrete mixes in a total of 29 batches of mixtures are presented. The concrete mixes had different water-to-cement ratios (w/...
The effects of aggregate characteristics on flow ability of mortar mixtures were investigated. Two types, five single sizes, and three gradations of fine aggregate were considered. Uncompacted voids of the aggregates were measured. Flow properties of 166 mortar batches made with the aggregates, together with different sand-to-cement ratios (s/c) an...
Concrete rheology is important because it affects the workability and uniformity of fresh concrete as well as the properties of the hardened concrete. In this dissertation, new models for predicting mortar and concrete rheological properties were developed. The present study includes both experimental and modeling work. In the experimental study, m...
A preliminary study has been conducted to evaluate the feasibility of using recycled concrete aggregate (RCA) in self-compacting concrete (SCC). Two different sources of RCA were collected and used in proportioning SCC with different levels of replacement of natural aggregate. Physical properties such as specific gravity, gradation, absorption and...