Hand book for Iowa Soldiers' and Sailors' Monument, 1898.

A narrative of the history of the Soldiers' and Sailor's Monument on the State Capitol grounds.

Self-Consolidating Concrete—Applications for Slip-Form Paving: Phase II, May 2011

The goal of the project was to develop a new type of self-consolidating concrete (SCC) for slip-form paving to simplify construction an make smoother pavements. Developing the new SCC involved two phases: a feasibility study (Phase I sponsored by TPF-5[098] and concrete admixtures industry) and an in-depth mix proportioning and performance study and field applications (Phase II). The phase I study demonstrated that the new type of SCC needs to possess not only excellent self-consolidating ability before a pavement slab is extruded, but also sufficient “green” strength (the strength of the concrete in a plastic state) after the extrusion. To meet these performance criteria, the new type of SCC mixtures should not be as fluid as conventional SCC but just flowable enough to be self-consolidating. That is, this new type of SCC should be semi-flowable self-consolidating concrete (SFSCC). In the phase II study, effects of different materials and admixtures on rheology, especially the thixotropy, and green strength of fresh SFSCC have been further investigated. The results indicate that SFSCC can be designed to (1) be workable enough for machine placement, (2) be self-consolidating without segregation, (3) hold its shape after extrusion from a paver, and (4) have performance properties (strength and durability) comparable with current pavement concrete. Due to the combined flowability (for self-consolidation) and shape-holding ability (for slip-forming) requirements, SFSCC demands higher cementitious content than conventional pavement concrete. Generally, high cementitious content is associated with high drying shrinkage potential of the concrete. However, well-proportioned and well-constructed SFSCC in a bike path constructed at Ames, IA, has not shown any shrinkage cracks after approximately 3 years of field service. On the other hand, another SFSCC pavement with different mix proportions and construction conditions showed random cracking. The results from the field SFSCC performance monitoring implied that not only the mix proportioning method but also the construction practice is important for producing durable SFSCC pavements. A carbon footprint, energy consumption, and cost analysis conducted in this study have suggested that SFSCC is economically comparable to conventional pavement concrete in fixed-form paving construction, with the benefit of faster, quieter, and easier construction.

Evaluation of the Argentine Nondestructive Test for Determining Concrete Compressive Strength, R-269 and MLR-75-2, 1975

The compressive strength of concrete is an important factor in the design of concrete structures and pavements. To assure the quality of the concrete placed at the project, concrete compressive cylinders are made at the jobsite. These cylinders undergo a destructive test to determine their compressive strength. However, the determination of concrete compressive strength of the concrete actually in the structure or pavement is frequently desirable. For this reason, a nondestructive test of the concrete is required. A nondestructive test of concrete compressive strength should be economical, easily performed by field personnel, and capable of producing accurate, reproducible results. The nondestructive test should be capable of detecting the extent of poor concrete in a pavement or structure due to improper handling, placement, or variations in mixing or materials.

Fly Ash Concrete Compressive Strength and Freeze-Thaw Durability, MLR-81-06, 1981

The current study investigated the effect of fly ash class, source and amount on the compressive strength and freeze-thaw durability of fly ash concrete. Concrete aggregates of varying quality were also included as test variables. The current results and those obtained from previous laboratory and field work indicate that compressive strength can·be affected by fly ash class, source and amount while aggregate quality is shown to have no effect on strength. Freeze-thaw durability of fly ash concrete is strongly affected by aggregate quality and to a lesser degree by fly ash class, amount and source.

Coarse Aggregate Gradations for P.C. Concrete, MLR-94-8, 1995

The effect of coarse aggregate gradation and cement content on strength of concrete was studied. Concrete made of Iowa Department of Transportation Standard Mix C-3 and Aggregate Gradation No. 3 were selected as reference. C-3 proportions were used for mixes #1 and #2. C-3 mix with 10% reduction of the cement content was used for mix #3. C-3 mix with 20% reduction of the cement content was used for mix #4. On the other hand, mix #1 used coarse aggregate of Gradation No. 3, while mixes #2, #3, and #4 used coarse aggregate mix of 65% concrete stone and 35% 3/8 in. chips. It was found that strengths of portland cement concrete decrease with decreasing cement factor. On the other hand, 35% of chip replacement for coarse aggregate increases strengths of concrete. By replacing 35% of coarse aggregate with chips, one could reduce cement factor 10% and achieve equivalent strengths.

Blanket Curing to Promote Early Strength Concrete, MLR-87-7, 1989

Fast Track concrete has proven to be successful in obtaining high early strengths. This benefit does not come without cost. Special Type III cement and insulating blankets to accelerate the cure add to its expense when compared to conventional paving. This research was intended to determine the benefit derived from the use of insulating blankets to accelerate strength gain in three concrete mixes using Type I cement. The goal was to determine mixes and curing procedures that would result in a range of opening times. This determination would allow the most economical design for a particular project by tailoring it to a specific time restraint. Three mixes of various cement content were tested in the field. Flexural beams were cast for each mix and tested at various ages. Two test sections were placed for each mix, one section being cured with the addition of insulating blankets and the other being cured with only conventional curing compound. Iowa Department of Transportation specifications require 500 psi flexural strength before a pavement can be opened to traffic. Concrete with Fast Track proportions (nominal 7 1/2 bag), Type I cement, and insulating blankets reached that strength in approximately 36 hr, a standard mix (nominal 6 1/2 bag) using the blankets in approximately 48 hr, and the Fast Track proportions with Type I cement without blankets in about 60 hr. The results showed a significant improvement in early strength gain with the use of insulating blankets.

New Method for Breaking High Strength Prestress Cable, MLR-97-6, 1997

A new method was developed for breaking high strength prestressed cable. The old method used an aluminum oxide grit packed into a special gripping jaw. The new method uses aluminum shims wrapped around the cable and then is gripped with a V-grip. The new method gives nearly 100% "good breaks" on the cable compared to approximately 10% good breaks with the old method. In addition, the new cable breaking method gives higher ultimate tensile strengths, is more reproducible, is quicker, cleaner and easier on equipment.

Evaluation of Concrete Patching Mixes and Opening Time Using the Maturity Concept, MLR-93-7, 1993

This report summarizes the findings of a research which was intended to evaluate the concrete strength and opening time for the full depth patching projects in Iowa under cold weather and whether or not cold water could be allowed in the mix. This research was performed both in the laboratory and in the field. The results indicated that with the present specification the concrete strength after five hours for two-lane patches which requires hot water and calcium chloride is about 1,600 psi. Hence, if a higher strength is desired, a longer curing time is required. Hot water will have to be used and water reducer is not recommended for two-lane patches. On the other hand, the concrete strength for multi-lane patches with either hot or cold water approaches 4,000 psi in less than 24 hours. There was only a slight difference in compressive strengths between the 24-hour and 36-hours curing times.

Strength-Temperature Study of Fly Ash Concrete, MLR-84-6, 1984

Class A, B, and C concrete paving mixes were tested for compressive strength at 40°F and 73°F, both with and without fly ash substitution for 15% of the portland cement. Two Class C ashes and one Class F ash from Iowa approved sources were examined in each mix. The purpose of the study was to provide data on cool weather strength development of concrete paving mixes utilizing Iowa materials. In all cases except one, the fly ash concretes exhibited lower 7 and 28- day compressive strengths at 40°F than control mixes. The continuation of the October 15 cut-off date for the use of fly ash concrete is recommended.

Void Ratio and Shear Strength of Two Compacted Crushed Stones, Progress Report, HR-99

Triaxial compression tests of two crushed limestones of differing highway service records indicate a fundamental difference in their shear strength -- void ratio relationship. Analyses were based on stress parameters at minimum sample volume, i.e., before there was significant sample dilation due to shear. The better service record sample compacted to higher density, and had a high effective angle of internal friction and zero effective cohesion. The other sample compacted to lower density and had a lower friction angle, but gained significant stability from effective cohesion. Repeated loading-unloading cycles reduced the cohesion, apparently due to modification of the sample structure. Extrapolations of the results to zero void ratio agree with sliding friction data reported on calcite, or with triaxial parameters reported on carbonate rocks.

Time-Temperature Strength-Reaction Product Relationships in Lime-Bentonite-Water Mixtures, HR-111, 1965

The interrelation of curing time, curing temperature, strength, and reactions in lime-bentonite-water mixtures was examined. Samples were molded at constant density and moisture content and then cured for periods of from 1 to 56 days at constant temperatures that ranged from 5C to 60C. After the appropriate curing time the samples were tested for unconfined compressive strength. The broken samples were then analyzed by x-ray diffractometer and spectrophotometer to determine the identity of the reaction products present after each curing period. It was found that the strength gain of lime-clay mixtures cured at different temperatures is due to different phases of the complex reaction, lime & clay to CSH(gel) to CSH(II) to CSH(I) to tobermorite. The farther the reaction proceeds, the higher the strength. There was also evidence of lattice substitutions in the structure of the calcium silicate hydrates at curing temperatures of 50C and higher. No consistent relationship between time, temperature, strength, and the S/A ration of reaction products existed, but in order to achieve high strengths the apparent C/S ration had to be less than two. The curing temperature had an effect on the strength developed by a given amount of reacted silica in the cured lime-clay mixture, but at a given curing temperature the cured sample that had the largest amount of reacted silica gave the highest strength. Evidence was found to indicate that during the clay reaction some calcium is indeed adsorbed onto the clay structure rather than entering into a pozzolanic reaction. Finally, it was determined that it is possible to determine the amount of silica and alumina in lime-clay reaction products by spectrophotometric analysis with sufficient accuracy for comparison purposes. The spectrophotometric analysis techniques used during the investigation were simple and were not time consuming.

New Method for Breaking High Strength Prestress Cable, MLR-97-6, 1997

A new method was developed for breaking high strength prestressed cable. The old method used an aluminum oxide grit packed into a special gripping jaw. The new method uses aluminum shims wrapped around the cable and then is gripped with a V-grip. The new method gives nearly 100% "good breaks" on the cable compared to approximately 10% good breaks with the old method. In addition, the new cable breaking method gives higher ultimate tensile strengths, is more reproducible, is quicker, cleaner and easier on equipment.

Pinpointing Suspect Triplicate Unconfined Compressive Strength Values in a Series of Soil-Additive Strength Determinations, HR-1, Progress Report, 1961

In recent years, various types of organic and inorganic materials have been investigated for use as soil stabilizing agents in the construction of highways and airports. Since the properties and environmental conditions of soils vary so greatly from place to place, a stabilizing agent that is suitable for one type of soil may not be satisfactory for another. As a result, it is often desirable to evaluate several stabilizing agents under varying treatment conditions before deciding on a specific one to be used with a given soil. In addition many research programs have been initiated which investigate the effects of these stabilizing agents upon soils.

The Flexural Fatigue Strength of Prestressed Steel I-Beams, HR-73, 1962

The purpose of this investigation was to study the flexural fatigue strength of two prestressed steel I-beams which had previously been fabricated in connection with a jointly sponsored project under the auspices of the Iowa State Highway Commission. The beams were prestressed by deflecting them under the action of a concentrated load at the center of a simple span, then welding unstressed high strength steel plates to the top and bottom flanges to retain a predetermined amount of prestress. The beams were rolled sections of A36 steel and the plates were USS "T-1" steel. Each of the two test specimens were subjected to an identical repeated loading until a fatigue failure occurred. The loading was designed to produce stresses equivalent to those which would have occurred in a simulated bridge and amounted to 84 percent of a standard H-15 live load including impact. One of the beams sustained 2,469,100 repetitions of load to failure and the other sustained 2,756,100 cycles. Following the fatigue tests, an experimental study was made to determine the state of stress that had been retained in the prestressed steel beams. This information, upon which the calculated stresses of the test could be superimposed, provided a method of correlating the fatigue strength of the beams with the fatigue information available on the two steels involved.

Investigation of Plastic Pipes for Highway Applications, HR-373A, Phase II, 1997

It is generally accepted that high density polyethylene pipe (HDPE) performs well under live loads with shallow cover, provided the backfill is well compacted. Although industry standards require carefully compacted backfill, poor inspection and/or faulty construction may result in soils that provide inadequate restraint at the springlines of the pipes thereby causing failure. The objectives of this study were: 1) to experimentally define a lower limit of compaction under which the pipes perform satisfactorily, 2) to quantify the increase in soil support as compaction effort increases, 3) to evaluate pipe response for loads applied near the ends of the buried pipes, 4) to determine minimum depths of cover for a variety of pipes and soil conditions by analytically expanding the experimental results through the use of the finite element program CANDE. The test procedures used here are conservative especially for low-density fills loaded to high contact stresses. The failures observed in these tests were the combined effect of soil bearing capacity at the soil surface and localized wall bending of the pipes. Under a pavement system, the pipes' performance would be expected to be considerably better. With those caveats, the following conclusions are drawn from this study. Glacial till compacted to 50% and 80% provides insufficient support; pipe failureoccurs at surface contact stresses lower than those induced by highway trucks. On the other hand, sand backfill compacted to more than 110 pcf (17.3 kN/m3) is satisfactory. The failure mode for all pipes with all backfills is localized wall bending. At moderate tire pressures, i.e. contact stresses, deflections are reduced significantly when backfill density is increased from about 50 pcf (7.9 kN/m^3) to 90 pcf (14.1 kN/m^3). Above that unit weight, little improvement in the soil-pipe system is observed. Although pipe stiffness may vary as much as 16%, analyses show that backfill density is more important than pipe stiffness in controlling both deflections at low pipe stresses and at the ultimate capacity of the soil-pipe system. The rate of increase in ultimate strength of the system increases nearly linearly with increasing backfill density. When loads equivalent to moderate tire pressures are applied near the ends of the pipes, pipe deflections are slighly higher than when loaded at the center. Except for low density glacial till, the deflections near the ends are not excessive and the pipes perform satisfactorily. For contact stresses near the upper limit of truck tire pressures and when loaded near the end, pipes fail with localized wall bending. For flowable fill backfill, the ultimate capacity of the pipes is nearly doubled and at the upper limit of highway truck tire pressures, deflections are negligible. All pipe specimens tested at ambient laboratory room temperatures satisfied AASHTO minimum pipe stiffness requirements at 5% deflection. However, nearly all specimens tested at elevated pipe surface temperatures, approximately 122°F (50°C), failed to meet these requirements. Some HDPE pipe installations may not meet AASHTO minimum pipe stiffness requirements when installed in the summer months (i.e. if pipe surface temperatures are allowed to attain temperatures similar to those tested here). Heating of any portion of the pipe circumference reduced the load carrying capacity of specimens. The minimum soil cover depths, determined from the CANOE analysis, are controlled by the 5% deflection criterion. The minimum soil cover height is 12 in. (305 mm). Pipes with the poor silt and clay backfills with less than 85% compaction require a minimum soil cover height of 24 in. (610 mm). For the sand at 80% compaction, the A36 HDPE pipe with the lowest moment of inertia requires a minimum of 24 in. (610 mm) soil cover. The C48 HDPE pipe with the largest moment of inertia and all other pipes require a 12 in. (305 mm) minimum soil cover.