Robust Methods for UHPC Early-Strength Determination and Quality Control for ABC

Project Information
Link to the Latest: September 2021 Progress Report

Background:

UHPC is one of the most commonly used or desired solution for ABC connections nowadays. With large initiatives for developing non-proprietary UHPC mixes (e.g. ABC-UTC ongoing imitative), the applications and use of UHPC for ABC are further expanding in the US and international markets. Given the ABC nature, many projects considering UHPC for connections and early bridge opening for traffic or following construction phases are hinging on reaching a desired early age strength. For example, bridge owners have recently specified Ductal JS1212 for projects requiring that 12 ksi strength is achieved at 12 hours. While robust mixes can accomplish this requirement, a reliable quality control method to verify such requirement on-site is still lacking. In remote sites, it becomes harder to verify the UHPC early age strength using the current state-of-practice, i.e. preparing cylinders by cutting and grinding the ends then testing them within 10-12 hours. In consultation with Caltrans among UHPC vendors and experts in relevant ACI committees, there is big interest in using two of the well-established methods for conventional concrete strength characterization for UHPC. These are using cubes as opposed to cylinders, and relying on strength maturity for quality control. No documented efforts have yet showed the feasibility of such methods for early strength determination of UHPC, which is the motivation of this project.

Objective:

The objectives of this project are to: (1) conduct comparative compression tests for various UHPC mixes and types using cubes and cylinders at early ages (as early as 10 hours); (2) develop strength maturity curves for various UHPC mixes and assess the reliability of using such curves for estimating UHPC early strength; (3) collect data from UHPC vendors (e.g. Steelike Inc.) on UHPC maturity to assemble a larger database; and (4) develop guidelines for UHPC quality control and assurance as pertains to early compression strength characterization.

Scope:
The following tasks will be performed to achieve the project objectives:
Task 1 – Literature Search

  • Summarize recent efforts in UHPC compressive strength characterization using maturity and cubes among other methods.

Task 2 – Comparative assessment of cubes versus cylinders for UHPC early strength characterization

  • The objective of this task is to conduct large number of UHPC cube and cylinder tests with various sizes, that ranges from 2 to 4 inches in diameter or cube side length, and at different ages (10-, 12-, 14-, 18-, and 24-hours, as well as 3-, 7-, 14-, and 28-days).

Task 3 – Establishing strength maturity large datasets using experimental testing and industry collaborations

  • The objective of this task is to relate UHPC early strength assessment to the strength maturity index and develop families of strength maturity curves for various UHPC mixes and range of strengths.

Task 4 – Develop quality control guidelines for UHPC early strength characterization

  • This task is intended to complement the extensive experimental works done in Tasks 2 and 3 to develop construction specifications and guidelines for UHPC early strength characterization using cubes and the SMM.

Task 5 – Final Report
Final report will be developed to summarize all research efforts along with ABC-UTC Guide for UHPC QC.

Research Team:
Principal Investigator: Dr. Mohamed Moustafa
Research Assistant: Mohammed Shaker Ibrahim

Previous Progress Reports: