The Relationship of Ferroan Dolomite Aggregate to Rapid Concrete Deterioration, HR-266, 1987

Some of Iowa's 13,200 miles of portland cement concrete (pcc) pavement have remained structurally sound for over 50 years while others have suffered premature deterioration. Research has shown that the type of coarse aggregate used in the pcc is the major cause of this premature deterioration. Some coarse aggregates for concrete exhibit a nonuniform performance history. They contribute to premature deterioration on heavily salted primary roadways while providing long maintenance-free life on unsalted secondary pavements. This inconsistency supports the premise that there are at least two mechanisms that contribute to the deterioration. Previous research has shown that one of these mechanisms is a bad pore system. The other is apparently a chemical reaction. The objective of this research is to develop simple rapid test methods to predict the durability of carbonate aggregate in pcc pavement. X-ray diffraction analyses of aggregate samples have been conducted on various beds from numerous quarries producing diffraction plots for more than 200 samples of dolomitic or dolomite aggregates. The crystalline structures of these dolomitic aggregates show maximum-intensity dolomite/ankerite peaks ranging from a d-spacing of 2.884 angstroms for good aggregates to a d-spacing of 2.914 angstroms for nondurable aggregates. If coarse aggregates with known bad pore systems are removed from this summary, the d-spacing values of the remaining aggregates correlate very well with expected service life. This may indicate that the iron substitution for magnesium in the dolomite crystal is associated with the instability of the ferroan dolomite aggregates in pcc pavement.

Investigation of Rapid Thermal Analysis Procedures for Prediction of the Service Life of PCCP Carbonate Coarse Aggregate, HR-337, 1993

The major objective of this research project was to use thermal analysis techniques in conjunction with x-ray analysis methods to identify and explain chemical reactions that promote aggregate related deterioration in portland cement concrete. Twenty-two different carbonate aggregate samples were subjected to a chemical testing scheme that included: • bulk chemistry (major, minor and selected trace elements) • bulk mineralogy (minor phases concentrated by acid extraction) • solid-solution in the major carbonate phases • crystallite size determinations for the major carbonate phases • a salt treatment study to evaluate the impact of deicer salts Test results from these different studies were then compared to information that had been obtained using thermogravimetric analysis techniques. Since many of the limestones and dolomites that were used in the study had extensive field service records it was possible to correlate many of the variables with service life. The results of this study have indicated that thermogravimetric analysis can play an important role in categorizing carbonate aggregates. In fact, with modern automated thermal analysis systems it should be possible to utilize such methods on a quality control basis. Strong correlations were found between several of the variables that were monitored in this study. In fact, several of the variables exhibited significant correlations to concrete service life. When the full data set was utilized (n = 18), the significant correlations to service life can be summarized as follows ( a = 5% level): • Correlation coefficient, r, = -0.73 for premature TG loss versus service life. • Correlation coefficient, r, = 0.74 for relative crystallite size versus service life. • Correlation coefficient, r, = 0.53 for ASTM C666 durability factor versus service life. • Correlation coefficient, r, = -0.52 for acid-insoluble residue versus service life. Separation of the carbonate aggregates into their mineralogical categories (i.e., calcites and dolomites) tended to increase the correlation coefficients for some specific variables (r sometimes approached 0.90); however, the reliability of such correlations was questionable because of the small number of samples that were present in this study.

The Role of Magnesium in Concrete Deterioration, HR-355, Appendix, 1994

In the main report concerning the role that magnesium may have in highway concrete aggregate, over 20,000 electron microprobe data were obtained, primarily from automated scans, or traverses, across dolomite aggregate grains and the adjacent cement paste. Representative traverses were shown in figures and averages of the data were presented in Table II. In this Appendix, detailed representative and selected analyses of carbonate aggregate only are presented. These analyses were not presented in the main report because they would be interesting to only a few specialists in dolomite· rocks. In this Appendix, individual point analyses of mineral compositions in the paste have been omitted along with dolomite compositions at grain boundaries and cracks. Clay minerals and quartz inclusions in the aggregate are also not included. In the analyses, the first three column headings from left to right show line number, x-axis, and y-axis (Line number is an artifact of the computer print-out for each new traverse. Consecutive line numbers indicate a continuous traverse with distances between each point of 1.5 to a few μ-m. X-axis and y-axis are coordinates on the electron microscope stage). The next columns present weight percent oxide content of FeO, K20, CaO, Si02, Al203, MgO, SrO, BaO, MnO, Na20, and C02 (calculated assuming the number of moles of C02 is equal to the sum of moles of oxides, chiefly CaO and MgO), TOTAL (the sum of all oxides), and total (sum of all oxides excluding COi). In many of the analyses total is omitted.

Factors Relating to Aggregate Durability in Portland Cement Concrete, HR-2022, Interim Report, 1983

Over the past several years we conducted a comprehensive study on the pore systems of limestones used as coarse aggregate in portland cement concrete (pee) and their relationship to freeze-thaw aggregate failure. A simple test called the Iowa Pore Index Test was developed and used to identify those coarse aggregates that had freeze-thaw susceptible pore systems. Basically, it identified those aggregates that could take on a considerable amount of water but only at a slow rate. The assumption was that if an aggregate would take on a considerable amount of water at a slow rate, its pore system would impede the outward movement of water through a critically saturated particle during freezing, causing particle fracture. The test was quite successful when used to identify aggregates containing susceptible pore systems if the aggregates were clean carbonates containing less than 2% or 3% insolubles. The correlation between service record, ASTM C666B and the pore index test was good, but not good enough. It became apparent over the past year that there were factors other than the pore system that could cause an aggregate to fail when used in pee. The role that silica and clay play in aggregate durability was studied.

Special Report on Alkali-Aggregate Reactivity in Iowa, MLR-80-03, 1980

The purpose of this investigation was to obtain information relative to the alkali-silica reaction in Iowa aggregates. Of particular concern were those aggregates in southwestern Iowa thought to be potentially alkali reactive. Further, should those aggregates have proven to be alkali-reactive, at what cement alkali content could these aggregates be considered to be deleteriously reactive? If the aggregates were proven to be reactive, what types of effects might show up in a structure in which an alkali-silica reaction has occurred? Also, what environmental conditions would cause the reaction? Finally, based on the information obtained from the investigation, would it be possible to raise the cement alkali content specifications? Would the Iowa DOT eliminate the alkali content limits altogether except for cement used with reactive aggregate in the same manner as AASHTO or ASTM? Also, would there be any other side effects that might occur as the result of using high alkali-cement?

Sieve Analysis of Combined Aggregate Samples by Different Test Methods, MLR-84-05, 1982

This past winter the sieve analysis of combined aggregate was investigated. This study was given No. 26 by the Central Laboratory. The purpose of this work was to try and develop a sieve analysis procedure for combined aggregate which is less time consuming and has the same accuracy as the method described in I.M. 304. In an attempt to use a variety of aggregates for this investigation, a request was made to each District Materials Office to obtain at least 3 different combined aggregate samples in their respective districts. At the same time it was also requested that the field technician test these samples, prior to submitting them to the Central Laboratory. The field technician was instructed to test each sample as described in method I.M. 304 and also by a modified AASHTO T27 method which will be identified in the report as Method A. The modified AASHTO Method A was identical to T27 with the exception that a smaller sample is used for testing. The field technicians submitted the samples, test results and also comments regarding the modified AASHTO procedure. The general comments of the modified AASHTO procedure were: The method was much simpler to follow; however, it took about the same amount of time so there was no real advantage. After reviewing AASHTO T27, T164, I.M. 304 and Report No. FHWA-RD-77-53 another test method was purposed. Report No. FHWA-RD-77-53 is a report prepared by FHWA from data they gathered concerning control practices and shortcut or alternative test methods for aggregate gradation. A second test method was developed which also was very similar to AASHTO T27, The test procedure for this method is attached and is identified as Method B. The following is a summary of test results submitted by the Field Technicians and obtained by the aggregate section of the Central Laboratory.

Effect of Compaction on the Aggregate Fracturing of Asphalt Concrete, MLR-86-07, 1986

Other states have elected not to adopt the 75 Blow Marshall Mix Design for their heavy traffic roads. Their reasons are that the 75 blow design cracks the larger aggregates. Therefore, a limited study was done during December, 1985, to try to determine what amount of cracking took place, and in what condition the cracks are in the mix.

Highway Applications for Rammed Aggregate Piers in Iowa Soils, TR-443, 2003

This report describes a study to evaluate Geopier® soil reinforcement technology in transportation construction. Three projects requiring settlement control were chosen for evaluation—an embankment foundation, a box culvert, and a bridge approach fill. For each project, construction observations, in situ soil testing, laboratory material characterization, and performance monitoring were carried out. For the embankment foundation project, Geopier elements were installed within and around an abutment footprint for the new I-35 overpass at the US Highway 5/Interstate 35 interchange in Des Moines, Iowa. Although the main focus of this investigation was to evaluate embankment foundation reinforcement using Geopier elements, a stone column reinforced soil provided an opportunity to compare systems. In situ testing included cone penetration tests (CPTs), pressuremeter tests (PMTs), Ko stepped blade tests, and borehole shear tests (BSTs), as well as laboratory material testing. Comparative stiffness and densities of Geopier elements and stone columns were evaluated based on full-scale modulus load tests and standard penetration tests. Vibrating wire settlement cells and total stress cells were installed to monitor settlement and stress concentration on the reinforcing elements and matrix soil. Settlement plates were also monitored by conventional optical survey methods. Results show that the Geopier system and the stone columns performed their intended functions. The second project involved settlement monitoring of a 4.2 m wide x 3.6 m high x 50 m long box culvert constructed beneath a bridge on Iowa Highway 191 south of Neola, Iowa. Geopier elements were installed to reduce total and differential settlement while ensuring the stability of the existing bridge pier foundations. Benefits of the box culvert and embankment fill included (1) ease of future roadway expansion and (2) continual service of the roadway throughout construction. Site investigations consisted of in situ testing including CPTs, PMTs, BSTs, and dilatometer tests. Consolidated drained triaxial compression tests, unconsolidated undrained triaxial compression test, oedometer tests, and Atterberg limit tests were conducted to define strength and consolidation parameters and soil index properties for classification. Vibrating wire settlement cells, total stress cells, and piezometers were installed for continuous monitoring during and after box culvert construction and fill placement. This project was successful at controlling settlement of the box culvert and preventing downdrag of the bridge foundations, but could have been enhanced by reducing the length of Geopier elements at the ends of the box culvert. This would have increased localized settlement while reducing overall differential settlement. The third project involved settlement monitoring of bridge approach fill sections reinforced with Geopier elements. Thirty Geopier elements, spaced 1.8 m apart in six rows of varying length, were installed on both sides of a new bridge on US Highway 18/218 near Charles City, Iowa. Based on the results of this project, it was determined that future applications of Geopier soil reinforcement should consider extending the elements deeper into the embankment foundation fill, not just the fill itself.

Determination and Evaluation of Alternate Methods for Managing and Controlling Highway-Related Dust, TR-449, 2002

Road dust is caused by wind entraining fine material from the roadway surface and the main source of Iowa road dust is attrition of carbonate rock used as aggregate. The mechanisms of dust suppression can be considered as two processes: increasing particle size of the surface fines by agglomeration and inhibiting degradation of the coarse material. Agglomeration may occur by capillary tension in the pore water, surfactants that increase bonding between clay particles, and cements that bind the mineral matter together. Hygroscopic dust suppressants such as calcium chloride have short durations of effectiveness because capillary tension is the primary agglomeration mechanism. Somewhat more permanent methods of agglomeration result from chemicals that cement smaller particles into a mat or larger particles. The cements include lignosulfonates, resins, and asphalt products. The duration of the cements depend on their solubility and the climate. The only dust palliative that decreases aggregate degradation is shredded shingles that act as cushions between aggregate particles. It is likely that synthetic polymers also provide some protection against coarse aggregate attrition. Calcium chloride and lignosulfonates are widely used in Iowa. Both palliatives have a useful duration of about 6 months. Calcium chloride is effective with surface soils of moderate fine content and plasticity whereas lignin works best with materials that have high fine content and high plasticity indices. Bentonite appears to be effective for up to two years and works well with surface materials having low fines and plasticity and works well with limestone aggregate. Selection of appropriate dust suppressants should be based on characterization of the road surface material. Estimation of dosage rates for potential palliatives can be based on data from this report, from technical reports, information from reliable vendors, or laboratory screening tests. The selection should include economic analysis of construction and maintenance costs. The effectiveness of the treatment should be evaluated by any of the field performance measuring techniques discussed in this report. Novel dust control agents that need research for potential application in Iowa include; acidulated soybean oil (soapstock), soybean oil, ground up asphalt shingles, and foamed asphalt. New laboratory evaluation protocols to screen additives for potential effectiveness and determine dosage are needed. A modification of ASTM D 560 to estimate the freeze-thaw and wet-dry durability of Portland cement stabilized soils would be a starting point for improved laboratory testing of dust palliatives.

Methods to Increase Durability of Reactive ("D" Cracking) Coarse Aggregate in Portland Cement Concrete, MLR-73-01, 1973

The coarse aggregates used for Portland Cement concrete in southwest Iowa have exhibited a poor serviceability. This early failure is attributed to a characteristic commonly referred as "D" cracking. "D" line cracking is a discolored area of concrete caused by many fine, parallel hairline cracks. "D" line cracking is primarily caused by the movement of water in and through coarse aggregate with a unique pore structure. The presence of the water in the aggregates at the time of freezing causes the "D" cracking to occur and early failure. By making the pore structure less permeable to moisture, it is thought the durability factor of the concrete should increase. By drying the aggregate before mixing and then mixing with the cement, the particles of cement should enter the outer pore structure, and upon hydration make the pore structure less permeable to moisture.

The Effect of Deicing Salt on Aggregate Durability, Progress Report HR-266, 1985

The Iowa DOT has been using rapid freezing in air and thawing in water to evaluate coarse aggregate durability in concrete since 1962. Earlier research had shown that the aggregate pore system was a major factor in susceptibility to D-cracking rapid deterioration. There are cases were service records show rapid deterioration of concrete containing certain aggregates on heavily salted primary roads and relatively good performance with the same aggregate in secondary pavements with limited use of deicing salt. A five-cycle salt treatment of the coarse aggregate prior to durability testing has yielded durability factors that correlate with aggregate service records on heavily salted primary pavements. X-ray fluorescence analyses have shown that sulfur contents correlate well with aggregate durabilities with higher sulfur contents producing poor durability. Trial additives that affect the salt treatment durabilities would indicate that one factor in the rapid deterioration mechanism is an adverse chemical reaction. The objective· of the current research is to develop a simple method of determining aggregate susceptibility to salt related deterioration. This method of evaluation includes analyses of both the pore system and chemical composition.

Investigation of Rapid Thermal Analysis Procedures for Prediction of the Service Life of PCCP Carbonate Coarse Aggregate: Phase I, Progress Report, HR-337, 1992

The major objective of this research project is to utilize thermal analysis techniques in conjunction with x-ray analysis methods to identify and explain chemical reactions that promote aggregate related deterioration in Portland cement concrete. The first year of this project has been spent obtaining and analyzing limestone and dolomite samples that exhibit a wide range of field service performance. Most of the samples chosen for the study also had laboratory durability test information (ASTM C 666, method B) that was readily available. Preliminary test results indicate that a strong relationship exists between the average crystallite size of the limestone (calcite) specimens and their apparent decomposition temperatures as measured by thermogravimetric analysis. Also, premature weight loss in the thermogravimetric analysis tests appeared to be related to the apparent decomposition temperature of the various calcite test specimens.

The Relationship of Aggregate Durability to Trace Element Content, Interim Report, HR-266, 1984

This report is a brief overview of the recent Iowa Department of Transportation research in the area of durability of Portland cement, concrete under the direction of Wendeli Dubberke. Present plans are to publish a more detailed report on low Portland cement concrete- durability research in January, 1985.