5 Sep 2024

Extending CEMHYD3D to Simulate Hydration of Portland Cement Pastes with High Volumes of Silica Fume

Abstract: Silica fume (SF) influences the hydration rate of Portland cement in differ-ent ways depending on the physical and chemical properties of the SF. This study reports the impact of SiO2 content (%), loss on ignition (%), and Brunauer–Emmett–Teller (BET) specific surface area on the hydration re-action of SF-cement paste mixtures. This study used five types of SFs with varying SiO2 content, loss on ignition (%), and particle morphology. Five SFs were mixed with Class H oil well cement at each of two different re-placement levels (20% or 30% by mass), and the released heat of hydra-tion was measured using isothermal calorimetry. The results were used to improve the pozzolanic reaction simulation feature of the original Virtual Cement and Concrete Testing Laboratory software, which enabled the soft-ware to simulate a higher SF replacement ratio in a cement mixture with higher fidelity. Results showed that a silica fume’s SiO2 content (%), loss on ignition (%), and BET specific surface area significantly influence the heat release rate. The new simulation model agrees well with the measure-ments on all the pastes tested.

29 May 2024

Finite Element, Petrographic, and Mechanical Analyses of Field-Cored Concrete Fairlead Beam Anchor Rods from Luke Air Force Base

Abstract: The fairlead beam is used to accomplish installation of the Barrier Arresting Kit 12 energy absorber for setback aircraft arresting system (AAS) installations at permanent operating facilities. Typical fairlead beams are affixed to a Portland cement concrete (PCC) foundation pad by a series of anchor assemblies made up of steel anchor rods set in grout inside galvanized pipe sleeves. US Air Force Civil Engineering Center (AFCEC) subject matter experts have identified a pattern of premature failures in these steel anchor assemblies when they are nondestructively inspected during AAS overhauls. The US Army Engineer Research and Development Center was tasked by AFCEC to investigate potential reasons for these premature failures. This report outlines methods and results of a finite element analysis of the anchorage, a visual and petrographic analysis of field-cored PCC anchor rods from Luke Air Force Base, and a mechanical analysis of specimens taken from the anchor rods within the PCC cores. Multiple modes of PCC distress were observed, and corrosion was evident in and around the anchor assemblies. Mechanical testing of specimens from the anchor rods indicated that an inferior grade of steel was used to fabricate these particular assemblies. Finally, observed deviations from design intention are discussed.

5 Apr 2023

4D Printing Structures for Extreme Temperatures Using Metakaolin Based Geopolymers

Abstract: Geopolymers (GPs) are a class of amorphous, aluminosilicate-based ceramics that cure at room temperature. GPs are formed by mixing an aluminosilicate source, which is metakaolin in this case, with an alkali activator solution, which can be either sodium or potassium water glass. GPs have attracted interest for use in structural applications over the past few decades because they have superior mechanical properties to ordinary Portland cement (OPC). Additionally, they can tolerate much higher temperatures and produce a fraction of the CO₂ compared to OPC. This project aims to develop geopolymer composites for 4D printing (the fourth dimension being time) and test their mechanical properties. Rheology and the effects of curing in ambient conditions will be evaluated for fresh geopolymer. Freeze-thaw resistance will be evaluated on potentially printable composites for extreme temperature resistance, etc.