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An Experimental Study on Evaluation of Creep and Shrinkage for Blast Furnace Slag-Cementless Concrete with Compressive Strength of 80 MPa
No full textIn this study, the long-term behavior of 80 MPa cementless concrete incorporating blast furnace slag and that of ordinary concrete with the same compressive strength were evaluated. The modulus of elasticity, autogenous shrinkage, and basic creep coefficient of the cementless concrete were found to be comparable to those of ordinary concrete. In contrast, the drying creep and drying shrinkage of the cementless concrete were observed to be lower than those of ordinary concrete
Real-Time Concrete Strength Estimation Using Electro-Mechanical Impedance and 1D CNN
No full textThis study presents a field-validated deep learning model for real-time, in-situ concrete strength estimation using piezoelectric sensors and electro-mechanical impedance (EMI) signal processing. Addressing the limitations of prior research—namely, narrow datasets and poor field applicability—we constructed a diverse database comprising over 775 data points across 28 mix designs and 107 sensor deployments. A novel 1D Convolutional Neural Network (1DCNN) with a baseline correction mechanism was developed to analyze time-series EMI signals. Our model achieved a mean absolute error of 2.68 MPa and an R² of 0.96 in testing, outperforming conventional methods. Transfer learning techniques further enhanced adaptability to new mix designs and sensor types. Most notably, the model was successfully validated using field data from highway pavement projects, demonstrating its robustness and real-world applicability. This work establishes a new benchmark for AI-driven concrete strength monitoring, bridging lab innovation and practical deployment
Towards Carbon-Neutrality in Concrete: The Role of Biochar in Air-Entrained and Non-Air-Entrained Systems as Sand Replacement
No full textBiochar is a carbon-rich solid residue resulting from the pyrolysis or devolatilization of waste biomass (e.g., wood chips, sawdust, grass) at elevated temperatures in an oxygen-limited furnace. Biochar provides an effective pathway for atmospheric CO2 removal via photosynthesis in biomass, which is subsequently converted to biochar while also producing energy. Due to its carbon-negative footprint (-2.4 to -2.9 kg CO2eq/ kg biochar), biochar could be used to reduce or eliminate the net CO2 emission of concrete. This study aims to produce low-carbon to carbon-negative concrete mixtures by utilizing biochar as a partial to total replacement of natural sand while leveraging its internal curing capacity to meet the performance requirements of workability, air content, and compressive strength of concrete. Specifically, concrete mixtures for two applications are produced: A non-air-entrained (NAE) concrete with 2500 psi minimum 28-day strength for basements, foundations, and walls not exposed to weather and an air-entrained (AE) concrete with 4000 psi minimum 28-day strength and 7% air content for pavements. Proper practices for the pre-treatment of biochar and mixture proportioning of biochar-augmented concrete will be shared
Development of Ternary Blended Cement Incorporating Limestone and Natural Pozzolan for Enhanced Durability and Sustainability
No full textThis study evaluates the commercial development of ternary blended cement with integration of a zeolite based natural pozzolan as a supplementary cementitious material (SCM). The experimental program involved a systematic characterization of the natural pozzolan, as well as assessment of fresh, mechanical and durability properties of the ternary blended cement to ascertain short-term and long-term performances
Rheological Evolution of Alkali-Activated Low-Grade Metakaolin Pastes
No full textThis study compares the rheological development of low-grade metakaolin clays mined from different geographical locations in the US. Small amplitude oscillatory shear (SAOS) is used to monitor the structural build-up of these alkali-activated pastes. Time sweeps of the storage modulus, loss modulus and the phase angle are used to understand their viscoelastic properties and determine their initial setting times. These results are validated with the ASTM Vicat needle test. Isothermal calorimetry is performed to link the rheological development of this cementitious system with its degree of hydration. The results indicate that the SAOS can prove to be a valuable testing method to characterize emerging low-carbon binders by offering a material-efficient, low-error alternative to traditional setting time tests while providing additional insights into their structural evolution
The Handy Rheometer: Capturing Complex Rheology with just a Camera and a Cylinder
No full textThe growing need for practical, on-site rheological tools in 3D concrete printing motivates this study, which introduces a low-cost, computer-vision based method for characterizing complex flow behavior. A simple experiment is performed by pulling a cylinder through a fresh cementitious suspension while recording the surface motion of a contrasted reference line on the suspension’s surface simply using a camera. A computer vision algorithm tracks the displacement field, enabling precise velocity profile extraction over time. By applying a moment balance to the two flow regions – Couette and Poiseuille – the flow is modeled as a Herschel-Bulkley fluid. This approach enables estimation of key rheological parameters, including yield stress, consistency, and flow index, from a single, portable experiment. The method bridges the gap between rheometer-based experiments and on-site quality control, offering a practical solution for assessing non-linear, shear-dependent properties critical to digital construction workflows
Computational Simulations Fresh-to-Solid Transition for Additive Manufacturing of Ultra-High-Performance Fiber Reinforced Concrete
No full textAdditive manufacturing of concrete is a topic of interest within the academia and industry. Simulating the printable concrete behavior from the fresh state to hardened state to long-term will provide the future engineers the ability to optimize the design and predict failure of structural elements. A key aspect for concrete additive manufacturing is the complexity of optimization which includes systems, schedule, and materials. Our research focus on the simulation fresh state, hardened behavior, and the transition from fluid-to-solid of nanoclay modified ERDC ultra-high-performance fiber reinforced concrete system. Discrete fresh concrete model (DFC) and Smooth Particle Hydrodynamics (SPH) model are studied to model the flow of fresh concrete from visco-elastic solid contact and non-Newtonian fluid perspectives. A new thixotropy model for the flow of 3D printed concrete is considered to model the rotational rheometer test, flow test, and direct shear test. DFC model flow is coupled with mathematical fiber orientation algorithm to generate fiber distribution and alignment according to the flow. Simulation of extrusion DFC particles from piston extruder and auger are performed to obtain extrusion shape and surface reconstruction was implemented. Lattice Discrete Particle Model (LDPM) using the 3D scan surface topography of 3D printed samples to study the effect of the surface features in the mechanical behavior of reinforced and unreinforced UHPC. Using data from Isothermal Calorimeter and Ultrasonic Pulse Velocity, a couple the DFC and LDPM model was developed which transitions the behavior between fluid to solid. This opens the pathway to optimize concrete 3D printing design
Upcycled Medical Hemp Fibers for Enhancing Tensile Strength and Fire Resistance of High-Strength Concrete
No full textThis research investigates fire and tensile resistance of high-strength concretes employing fibers extracted from waste medical hemp stalks. Environmental impact analysis of hemp-based solutions is also considered
The Effect of Cracks on the Corrosion Distribution along Rebar in a Chloride Contaminated Concrete
No full textCracks in concrete allows the ingress of corrosive factors such as chloride ions, water, and oxygen, and reduce the durability of the structure. Therefore, the generation and the development of the cracks must be controlled within the extent with which they do not affect the durability. However, the influences of crack on the steel bar corrosion are still poorly understood. Therefore, in order to investigate how the ingress of corrosion factors through cracks affects rebar corrosion and corrosion distribution, accelerated deterioration tests simulating a chloride rich environment were conducted in this study, using bending crack width and corrosion acceleration period as parameters. This study reports the results up to 3 months of corrosion acceleration period. As a result, it was observed that the cracks facilitated the ingress of chloride ions into the concrete. However, the effect of the cracks to ease the penetration of chloride faded with time. As for the corrosion of the steel bars, the effect of the presence of cracks was observed, but the effect of the width of the cracks was not observed. As the corrosion acceleration period was extended, the corroded area of the rebar also expanded, and the corrosion distribution changed. At the early period, localised cross-sectional reduction was observed around cracks, but later, the corrosion became more extensive, and the reduction in cross-sectional area spread along entire rebar
Sulfate Addition to Ground Granulated Blast-furnace Slag for use as a Supplementary Cementitious Material in Concrete
No full textThe drive towards net-zero carbon emissions within the cement and concrete industry has seen the utilisation of lower embodied carbon materials such as ground granulated blast-furnace slag (GGBS). This can however lead to overlooking the technical performance of such materials. Current EN standards restrict additions to GGBS, limiting the sulfate optimisation of the aluminate rich material and thus potentially impacting the performance of the resultant concrete. In the UK and Ireland, GGBS is generally added as a supplementary cementitious material (SCM) to the concrete mixer opposed to inter-grinding or blending in a binary or ternary cementitious system. Although practical in terms of varying the replacement rate, this can lead to under-sulfated concrete due to the dilution of calcium sulfate (CaSO4) in the cement with increasing replacement percentage of GGBS. This study aimed to assess the suitable amounts of sulfate to balance the aluminate content in concrete while using commercially available GGBS as a SCM. As the alumina content plays a pivotal role in durability against sulfate attack and mechanical strength of GGBS concrete, a slag with a high alumina content (15%) was used at varying CaSO4 additions in cement replacement values of 30% and 70%. Measurement of these performance characteristics was carried out and compared to non-sulfated specimens. It was found that the addition of CaSO4 at optimal dosages improved sulfate resistance. Durability however was hindered when the sulfate demand was not met, due to effect on the capillary pressures within the pore structure and formation of alumina-based hydration products. The impact on compressive strength was more evident at a higher replacement due to the activation effect of CaSO4. An optimal CaSO4 addition provides enough sulfate to regulate the C3A in cement with suitable volume remaining to promote C3S hydration phases for improved early age strength