The demand for cement is increasing, and the Illinois Department of Transportation (IDOT) realized that this growing demand would have to be met by increased domestic production or by overseas supplements. IDOT wished to explore the feasibility of increasing cement production by exceeding the established ASTM C150 and C465 limits for limestone additions, while adhering to requirements to reduce CO2 emissions.
To enable the use of more sustainable materials for use in concrete pavements, overlays, and bridge decks, IDOT funded a study conducted by the Illinois Center for Transportation (ICT) to investigate the viability of these proposed changes and their effects on concrete performance. The aim of the study was to evaluate the strength and durability characteristics of concrete made with modified Portland cement containing higher quantities of limestone and inorganic process additions (such as granulated blast furnace slag and fly ash) and higher amounts of insoluble residue.
Twenty-four concrete mix batches with different cementitious combinations and aggregates were developed for the study. Each cement source was batched in a concrete mixture by replacing 30% of the total cement content with supplementary cementitious materials, fly ash, or slag. Also, each cementitious combination was batched with fine aggregates and with coarse aggregate (limestone).
Mohsen Issa, professor in the Department of Civil and Materials Engineering, University of Illinois at Chicago (UIC), served as lead investigator of the study. He says the results showed that increasing the amount of limestone and inorganic process additions in cement in quantities exceeding 5% by weight and an increase of insoluble residue to 1.5% had negligible effects on the strength and durability properties of the concrete. Similar performance was observed in the concrete mixes with modified and conventional cement.
John Huang, who served as the chair of the IDOT Technical Review Panel for the project, adds that although the cements with higher amounts of limestone had lower “early-age” strength, they still exceeded IDOT’s 14-day requirement for minimum compressive and flexural strengths. “On the basis of these findings, IDOT revised its specifications for the maximum limits of limestone addition to cement and created a new label, Type 11, for that cement.”
At the time of the study, Mr. Huang, now retired, was Acting Mixture Control Engineer for IDOT District 1, Bureau of Materials, headquartered in Schaumburg.
Mr. Huang also sees additional, future benefits from this study: “If IDOT is faced with finding sustainable, financially suitable solutions to cement production, it can count on technical support and joint cooperation from the local ‘ready-mix’ community; regional cement, fly ash, and slag suppliers; and the civil engineering department at UIC.”
The title of the study was “Effect of Portland Cement (Current ASTM C150/AASHTO M85) with Limestone and Process Addition (ASTM C465/AASHTO M327) on the Performance of Concrete for Pavement and Bridge Decks” (Project R27-112). The full report is available on ICT’s website.