School of Civil and Environmental Engineering

Ph.D. Thesis Defense Announcement

Hydration and Microstructural Development of Portland Limestone Cement-Based Materials

By

Elizabeth I. Nadelman

Advisor:

Dr. Kimberly Kurtis (CEE)

Committee Members:

Dr. Lawrence Kahn (CEE), Dr. Susan Burns (CEE),

Dr. T. Russell Gentry (ARCH) and Dr. Carsten Sievers (ChBE)

Date & Time: June 8, 2016,  9:00 am

Location: Jesse W.  Mason Conference Room  2119

With more than 34 billion tonnes of portland cement concrete placed in 2015, the manufacture of portland cement is estimated to contribute 5-8% of all anthropogenic carbon dioxide (CO2) emissions each year. While several strategies have been proposed to curb the CO2 emissions associated with cement manufacture, one of the most immediately applicable and economically viable options is to reduce the amount of clinker in portland cement by replacing a portion of it with a widely available mineral filler, such as limestone. The objective of this research is to examine the relative influences of the limestone's composition, blending rate with portland cement, and particle size distribution on the hydration, microstructural development, and long-term durability of limestone-blended cement-based materials.

Investigation into the early-age hydration kinetics of portland limestone cements (PLCs) revealed that hydration rate was primarily dependent upon the fineness of the cement, with PLCs ground significantly finer than ordinary portland cements (OPCs) exhibiting increased rates and degrees of hydration as a result of heterogeneous nucleation effects, and PLCs ground to similar a fineness as OPCs exhibiting similar or decreased rates and degrees of hydration as a result of dilution effects. Experimental and computational studies on chemical shrinkage further found that the chemical shrinkage of finely ground PLCs is increased at early ages due to the accelerated rate of hydration and at later ages and degrees of hydration due to chemical interactions between the limestone and the cement clinker. Such results suggest that concrete produced from PLCs - especially those that are finely ground - may be more susceptible to cracking at early ages. Assessment of microstructural development revealed that dilution of the clinker by limestone increased the total porosity of the cement paste matrix, while improvements to particle packing by filler effects reduced the average size of the pores. The net effect was that PLC concretes had similar permeabilities to OPC concretes. When combined with supplementary cementitious materials (SCMs), chemical interactions between the limestone and the SCMs further reduced the porosity of the PLC concretes, leading to additional reductions in permeability than compared to OPC-SCM blended concretes. Overall, the findings suggest that while hydration mechanics are altered in PLC-based materials, their long-term durability is comparable to those of OPC-based materials, provided that the increases to chemical shrinkage do not cause increased cracking at very early ages.