Optimization of Soil Stabilization with Class C Fly Ash, January 1987

Previous Iowa DOT sponsored research has shown that some Class C fly ashes are ementitious (because calcium is combined as calcium aluminates) while other Class C ashes containing similar amounts of elemental calcium are not (1). Fly ashes from modern power plants in Iowa contain significant amounts of calcium in their glassy phases, regardless of their cementitious properties. The present research was based on these findings and on the hyphothesis that: attack of the amorphous phase of high calcium fly ash could be initiated with trace additives, thus making calcium available for formation of useful calcium-silicate cements. Phase I research was devoted to finding potential additives through a screening process; the likely chemicals were tested with fly ashes representative of the cementitious and non-cementitious ashes available in the state. Ammonium phosphate, a fertilizer, was found to produce 3,600 psi cement with cementitious Neal #4 fly ash; this strength is roughly equivalent to that of portland cement, but at about one-third the cost. Neal #2 fly ash, a slightly cementitious Class C, was found to respond best with ammonium nitrate; through the additive, a near-zero strength material was transformed into a 1,200 psi cement. The second research phase was directed to optimimizing trace additive concentrations, defining the behavior of the resulting cements, evaluating more comprehensively the fly ashes available in Iowa, and explaining the cement formation mechanisms of the most promising trace additives. X-ray diffraction data demonstrate that both amorphous and crystalline hydrates of chemically enhanced fly ash differ from those of unaltered fly ash hydrates. Calciumaluminum- silicate hydrates were formed, rather than the expected (and hypothesized) calcium-silicate hydrates. These new reaction products explain the observed strength enhancement. The final phase concentrated on laboratory application of the chemically-enhanced fly ash cements to road base stabilization. Emphasis was placed on use of marginal aggregates, such as limestone crusher fines and unprocessed blow sand. The nature of the chemically modified fly ash cements led to an evaluation of fine grained soil stabilization where a wide range of materials, defined by plasticity index, could be stabilized. Parameters used for evaluation included strength, compaction requirements, set time, and frost resistance.

Development of a Conductometric Test for Frost Resistance of Concrete, HR-272, 1988

Research is described that was aimed at developing a test method which can be reasonably and rapidly performed in the laboratory and in the field to predict, with a high degree of certainty, the behavior of concrete subjected to the action of alternate freezing and thawing. The conductometric evaluation of concrete durability was explored with 3 different test methods: conductometric evaluation of the resistance of concrete to rapid freezing and thawing; conductomtric evaluation of the resistance of concrete to natural freezing and thawing, and conductometric evaluation of the pore size distribution of concrete and its correlation to concrete durability. The study showed that conductance could be used as a viable method for determining the durability of portland cement concrete. This would also allow the continuous monitoring of concrete durability without the removal twice per week from the freeze/thaw chamber. Recommendations for the continued development of these test methods are also included.

Laboratory Testing of SHRP SPS-2 P.C.C. Mixes, MLR-94-5, 1995

This research evaluated the concrete strength of two mixes which were used in the Polk County project NHS-500-1(3)--10-77 and were developed to meet a contract requirement of 900 psi third-point 28-day flexural strength. Two concrete mixes, the Proposed Mix and the Enhanced Mix, were tested for strength. Based on the experimental results, it was found that the addition of 50 lb of cementitious materials did not significantly increase concrete strength. The requirement of 900 psi 28-day third-point flexural strength (MOR-TPL) was not achieved by this amount of addition of cementitious materials.

An Evaluation of the Troxler 3241-B Nuclear Asphalt Gauge, MLR-85-11, 1986

The Troxler 3241-B Asphalt Content Gauge is intended for rapidly determining the bitumen content of bituminous paving mixtures. A 300 Millicurie Americuium 241: Beryllium source emitts neutrons which are affected by the hydrogen in the mix. The affected neutrons are detected by Helium 3 detectors, counted and computed into a percentage bitumen of the asphalt mix. The current methods of determining the bitumen content of bituminous paving mixtures requires the use of potentially hazardous chemicals and several hours of testing time. When extracted aggregates are not needed, determination of the bitumen content of a paving mixture by the nuclear method may be easier, quicker and potentially safer. The objective of the project is to study the accuracy of the Troxler 3241-B Nuclear Asphalt Content Gauge in measuring the asphalt cement (AC) content of asphalt concrete mixtures produced with different asphalt cements and different aggregates.

Development of a Conductometric Test for Frost Resistance of Concrete, HR-272, Phase II, 1986

The purpose of this report is to describe the major research activities during the period of February 1, 1985 - October 30, 1986 for the Iowa Highway Research Board under the research contract entitled "Development of a Conductometric Test for Frost Resistance of Concrete." The objective of this research, as stated in the project proposal, is to develop a test method which can be reasonably rapidly performed in the laboratory and in the field to predict the behavior of concrete subjected to the action of alternate freezing and thawing with a high degree of certainty. In the work plan of the proposal it was stated that the early part of the first year would be devoted to construction of testing equipment and preparation of specimens and the remainder of the year would be devoted to the testing of specimens. It was also stated that the second and third years would be devoted to performance and refinements of tests, data analysis, preparation of suggested specifications, and performance of tests covering variables which need to be studied such as types of aggregates, fly ash replacements and other admixtures. The objective of this report is to describe the progress made during the first 20 months of this project and assess the significance of the results obtained thus far and the expected significance of the results obtainable during the third year of the project.