Field Evaluation of Cold In-Place Recycling of Asphalt Concrete, HR-303, 1993

The average thickness of the existing asphalt cement concrete (ACC) along route E66 in Tama County was 156 mm (6.13 in.). The rehabilitation strategy called for widening the base using the top 75 mm (3 in.) of the existing ACC by a recycling process involving cold milling and mixing with additional emulsion/rejuvenator. The material was then placed into a widening trench and compacted to match the level of the milled surface. The project had the following results: (1) Cold recycled ACC pavement provided adequate pavement structure for a low volume road; (2) Premature cracking of the ACC in the widened pavement area was caused by compaction of the mix over a saturated subgrade; and (3) Considerably less transverse and longitudinal cracking was observed with 75 mm (3 in.) of cold recycled ACC and a 50 mm (2 in.) hot mix ACC overlay than with a conventional hot mix overlay with no cold recycling. More research should be done on efficient construction procedures and incorporating longer test sections for proper evaluation.

Control of Concrete Deterioration Due to Trace Compounds in Deicers, HR-299, 1992

This report describes the research completed under the research contract entitled "Development of a Conductometric Test for Frost Resistance of Concrete" undertaken for the Iowa Highway Research Board. The objective of the project was to develop 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 significance of the results obtained, and recommendations for use and the continued development of conductometric testing are presented in this final report. In this project the conductometric evaluation of concrete durability was explored with three different test methods. The test methods and procedures for each type of test as well as presentation of the results obtained and their significance are included in the body of the report. The three test methods were: (1) Conductometric evaluation of the resistance of concrete to rapid freezing and thawing, (2) Conductometric evaluation of the resistance of concrete to natural freezing and thawing, and (3) Conductometric evaluation of the pore size distribution of concrete and its correlation to concrete durability. The report also includes recommendations for the continued development of these test methods.

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

Concretes with service lives of less than 15 years and those with lives greater than 40 years were studied with petrographic microscope, scanning electron microscope, and electron microprobe to determine why these two groups of concrete exhibit such different degrees of durability under highway conditions. Coarse aggregate used in both types of concrete were from dolomite rock, but investigation revealed that dolomite aggregate in the two groups of concretes were much different in several respects. The poorly-performing aggregate is fine-grained, has numerous euhedral and subhedral dolomite rhombohedra, and has relatively high porosity. Aggregate from durable concrete is coarse-grained, with tightly interlocked crystal fabric, anhedral dolomite boundaries, and low porosity. Aggregate in short service life concrete was found to have undergone pervasive chemical reactions with the cement which produced reaction rims on the boundaries of coarse aggregate particles and in the cement region adjacent to aggregate boundaries. Textural and porosity differences are believed to be chiefly responsible for different service lives of the two groups of concrete. The basic reaction that has occurred in the short service life concretes between coarse aggregate and cement is an alkali-dolomite reaction. In the reaction dolomite from the aggregate reacts with hydroxide ions from the cement to free magnesium ions and carbonate ions, and the magnesium ions precipitate as brucite, Mg(OH)2. Simultaneously with this reaction, a second reaction occurs in which product carbonate ions react with portlandite from the cement to form calcite and hydroxide ions. Crystal growth pressures of newly formed brucite and calcite together with other processes, e.g. hydration state changes of magnesium chloride hydrates, lead to expansion of the concretes with resultant rapid deterioration. According to this model, magnesium from any source, either from reacting dolomite or from magnesium road deicers, has a major role in highway concrete deterioration. Consequently, magnesium deicers should be used with caution, and long-term testing of the effects of magnesium deicers on highway concrete should be implemented to determine their effects on durability.

Lightweight Aggregate Use in Structural Concrete, MLR-69-1 and R-229, 1969

The Iowa State Highway Commission has adopted a number of rigid safety requirements that the Bureau of Public Roads has set forth as standards for road construction. One of these safety requirements is the elimination of two piers on Interstate grade separations, thus leaving two long spans. These longer spans lower the ability of prestressed concrete beams to compete economically with steel beams. In an effort to be more competitive, the prestressing companies have been studying the use of lightweight aggregate in structural concrete.

Tutkimusmetodologia ja sen kehittäminen opettajan käyttöteorian ja opetuksen välisen suhteen tutkimuksessa

Summary: Research methodology and its development in the study of the relationship between a teacher's practical theory and teaching practices

Effect of Mix Times on PCC Properties, HR-1066, 1998

The objectives of this research were the collection and evaluation of the data pertaining to the importance of concrete mixing time on air content and distribution, consolidation and workability for pavement construction. American Society for Testing and Materials (ASTM) standard C 94 was used to determine the significance of the mixing time on the consistency of the mix being delivered and placed on grade. Measurements of unit weight, slump, air content, retained coarse aggregate and compressive strength were used to compare the consistency of the mix in the hauling unit at the point of mixing and at the point placement. An analysis of variance was performed on the data collected from the field tests. Results were used to establish the relationship between selected mixing time and the portland cement concrete properties tested. The results were also used to define the effect of testing location (center and side of truck, and on the grade) on the concrete properties. Compressive strength test concepts were used to analyze the hardened concrete pavement strength. Cores were obtained at various locations on each project on or between vibrator locations to evaluate the variance in each sample, between locations, and mixing times. A low-vacuum scanning electron microscope (SEM) was used to study air void parameters in the concrete cores. Combining the data from these analysis thickness measurements and ride in Iowa will provide a foundation for the formulation of a performance based matrix. Analysis of the air voids in the hardened concrete provides a description of the dispersion of the cemtitious materials (specifically flyash) and air void characteristics in the pavement. Air void characteristics measured included size, shape and distribution.

Composite Precast Prestressed Concrete Bridge Slabs, HR-310, 1991

Precast prestressed concrete panels have been used as subdecks in bridge construction in Iowa and other states. To investigate the performance of these types of composite slabs at locations adjacent to abutment and pier diaphragms in skewed bridges, a research prcject which involved surveys of design agencies and precast producers, field inspections of existing bridges, analytical studies, and experimental testing was conducted. The survey results from the design agencies and panel producers showed that standardization of precast panel construction would be desirable, that additional inspections at the precast plant and at the bridge site would be beneficial, and that some form of economical study should be undertaken to determine actual cost savings associated with composite slab construction. Three bridges in Hardin County, Iowa were inspected to observe general geometric relationships, construction details, and to note the visual condition of the bridges. Hairline cracks beneath several of the prestressing strands in many of the precast panels were observed, and a slight discoloration of the concrete was seen beneath most of the strands. Also, some rust staining was visible at isolated locations on several panels. Based on the findings of these inspections, future inspections are recommended to monitor the condition of these and other bridges constructed with precast panel subdecks. Five full-scale composite slab specimens were constructed in the Structural Engineering Laboratory at Iowa State University. One specimen modeled bridge deck conditions which are not adjacent to abutment or pier diaphragms, and the other four specimens represented the geometric conditions which occur for skewed diaphragms of 0, 15, 30, and 40 degrees. The specimens were subjected to wheel loads of service and factored level magnitudes at many locations on the slab surface and to concentrated loads which produced failure of the composite slab. The measured slab deflections and bending strains at both service and factored load levels compared reasonably well with the results predicted by simplified Finite element analyses of the specimens. To analytically evaluate the nominal strength for a composite slab specimen, yield-line and punching shear theories were applied. Yield-line limit loads were computed using the crack patterns generated during an ultimate strength test. In most cases, these analyses indicated that the failure mode was not flexural. Since the punching shear limit loads in most instances were close to the failure loads, and since the failure surfaces immediately adjacent to the wheel load footprint appeared to be a truncated prism shape, the probable failure mode for all of the specimens was punching shear. The development lengths for the prestressing strands in the rectangular and trapezoidal shaped panels was qualitatively investigated by monitoring strand slippage at the ends of selected prestressing strands. The initial strand transfer length was established experimentally by monitoring concrete strains during strand detensioning, and this length was verified analytically by a finite element analysis. Even though the computed strand embedment lengths in the panels were not sufficient to fully develop the ultimate strand stress, sufficient stab strength existed. Composite behavior for the slab specimens was evaluated by monitoring slippage between a panel and the topping slab and by computation of the difference in the flexural strains between the top of the precast panel and the underside of the topping slab at various locations. Prior to the failure of a composite slab specimen, a localized loss of composite behavior was detected. The static load strength performance of the composite slab specimens significantly exceeded the design load requirements. Even with skew angles of up to 40 degrees, the nominal strength of the slabs did not appear to be affected when the ultimate strength test load was positioned on the portion of each slab containing the trapezoidal-shaped panel. At service and factored level loads, the joint between precast panels did not appear to influence the load distribution along the length of the specimens. Based on the static load strength of the composite slab specimens, the continued use of precast panels as subdecks in bridge deck construction is recommended.

Lateral Load Resistance of Diaphragms in Prestressed Concrete Girder Bridges, HR-319, 1991

Each year several prestressed concrete girder bridges in Iowa and other states are struck and damaged by vehicles with loads too high to pass under the bridge. Whether or not intermediate diaphragms play a significant role in reducing the effect of these unusual loading conditions has often been a topic of discussion. A study of the effects of the type and location of intermediate diaphragms in prestressed concrete girder bridges when the bridge girder flanges were subjected to various levels of vertical and horizontal loading was undertaken. The purpose of the research was to determine whether steel diaphragms of any conventional configuration can provide adequate protection to minimize the damage to prestressed concrete girders caused by lateral loads, similar to the protection provided by the reinforced concrete intermediate diaphragms presently being used by the Iowa Department of Transportation. The research program conducted and described in this report included the following: A comprehensive literature search and survey questionnaire were undertaken to define the state-of-the-art in the use of intermediate diaphragms in prestressed concrete girder bridges. A full scale, simple span, restressed concrete girder bridge model, containing three beams was constructed and tested with several types of intermediate diaphragms located at the one-third points of the span or at the mid-span. Analytical studies involving a three-dimensional finite element analysis model were used to provide additional information on the behavior of the experimental bridge. The performance of the bridge with no intermediate diaphragms was quite different than that with intermediate diaphragms in place. All intermediate diaphragms tested had some effect in distributing the loads to the slab and other girders, although some diaphragm types performed better than others. The research conducted has indicated that the replacement of the reinforced concrete intermediate diaphragms currently being used in Iowa with structural steel diaphragms may be possible.

Estudio sobre los procesos de integración laboral de los inmigrantes. Study of immigrants' labour integration process

El presente trabajo pretende mostrar los resultados de un estudio cuya intención era identificar posibles variables que afectan a los procesos y estrategias de integración laboral de personas procedentes de otros países; las necesidades formativas en relación al colectivo de referencia y ampliar el conocimiento del fenómeno en aras de la intervención psicoeducativa y social. A partir de una metodología de investigación de orientación cualitativa se ha concluido que las diferencias en cuanto a las estrategias de integración y sus logros están más determinadas por los niveles de cualificación en el país de origen que por las propias diferencias culturales. The article shows the results of a study carried out by the authors to identify possible variables that affect the processes and strategies of occupational integration of people coming from other countries, to establish training needs in relation to the reference group and to extend the knowledge of the phenomenon for the sake of the educational and social intervention. Using a qualitative research methodology, it was concluded that the differences in integration strategies and their accomplishments are better explained by the levels of qualification attained in the country of origin than by cultural differences.

Estudio sobre los procesos de integración laboral de los inmigrantes. Study of immigrants' labour integration process

El presente trabajo pretende mostrar los resultados de un estudio cuya intención era identificar posibles variables que afectan a los procesos y estrategias de integración laboral de personas procedentes de otros países; las necesidades formativas en relación al colectivo de referencia y ampliar el conocimiento del fenómeno en aras de la intervención psicoeducativa y social. A partir de una metodología de investigación de orientación cualitativa se ha concluido que las diferencias en cuanto a las estrategias de integración y sus logros están más determinadas por los niveles de cualificación en el país de origen que por las propias diferencias culturales. The article shows the results of a study carried out by the authors to identify possible variables that affect the processes and strategies of occupational integration of people coming from other countries, to establish training needs in relation to the reference group and to extend the knowledge of the phenomenon for the sake of the educational and social intervention. Using a qualitative research methodology, it was concluded that the differences in integration strategies and their accomplishments are better explained by the levels of qualification attained in the country of origin than by cultural differences.

Asphalt Cement Concrete Longitudinal Joint Adhesive Crafco PN 34524 (Iowa DOT New Product C-98-7), HR-2084, 2000

The joint between two lanes of asphalt pavement is often the first area of a roadway which shows signs of deterioration and requires maintenance. As the final lift of hot asphalt is being placed in a construction project, it is being forced p against the adjoining lane of cold asphalt, forming the longitudinal joint. The mating of the two lanes, to form a high quality seal, is often not fully successful and later results in premature stripping or raveling as water enters the unsealed joint. The application of a hot poured rubberized asphaltic joint sealant along the joint face in the final stage of construction should help to form a watertight joint seal. A new product, especially formulated for the longitudinal joint in asphalt pavements was proposed to improve joint sealing. The following describes the experimental application of the new product, Crafco, PN 34524.

Minimum VMA in HMA Based on Gradation and Volumetric Properties, MLR-95-7, 1996

The use of voids in the mineral aggregate (VMA) criteria for proper mix design of hot mix asphalt (HMA) mixtures is a time honored and fairly successful tool. Recent developments in the field of asphalt mix design have encouraged the use of mixtures with a coarse aggregate structure to resist the affect of heavy traffic loads. By using the equations presented, which account for both aggregate gradation and the volumetric properties of the materials, the mix designer is able to judge the proper VMA requirement for each unique blend of materials. By applying the new equations, the most economical mix may be selected without great risk of reduced durability. Supporting data from field application is presented to illustrate the use of the equations.

A Study of the Reliability of the ASTM C-666 Freeze-Thaw Test, MLR-72-01 and R-252, 1972

The Iowa State Highway Commission purchased a Conrad automatic freeze and thaw machine and placed it in operation during October 1961. There were a few problems, but considering, the many electrical and mechanical devices used in the automatic system it has always functioned quite well. Rapid freezing and thawing of 4"x4"xl8" concrete beams has been conducted primarily in accordance with ASTM C-29l (now ASTM C-666 procedure B) at the rate of one beam per day. Over 4000 beams have been tested since 1961, with determination of the resulting durability factors. Various methods of curing were used and a standard 90 day moist cure was selected. This cure seemed to yield durability factors that correlated very well with ratings of coarse aggregates based on service records. Some concrete beams had been made using the same coarse aggregate and the durability factors compared relatively well with previous tests. Durability factors seemed to yield reasonable results until large variations in durability factors were noted from beams of identical concrete mix proportions in research projects R-234 and R-247. This then presents the question "How reliable is the durability as determined by ASTM C-666?" This question became increasingly more important when a specification requiring a minimum durability factor for P.C. concrete made from coarse aggregates was incorporated into the 1972 Standard Specification for coarse aggregates for concrete.

Heat Dissipation and Crack Control in Massive Concrete at the Burlington Bridge, MLR-94-1, 1995

The large concrete placements at the Burlington Bridge were expected to cause great temperature differentials within the individual placements. In an attempt to reduce cracking due to the large temperature differentials, the Iowa Department of Transportation required that contractors continuously monitor the temperatures and temperature differentials in the concrete placement to assure that the temperature differentials did not exceed 35 deg F. It was felt that if temperature differentials remained below 35 deg F, cracking would be minimized. The following is a summary of the background of the project, and what occurred during individual concrete placements. The following conclusions were drawn: 1) Side temperatures are cooler and more greatly affected by ambient air temperatures; 2) When the 35 deg F limit was exceeded, it was almost exclusively the center to side differential; 3) The top temperature increases substantially when a new pour is placed; 4) The use of ice and different cement types did seem to affect the overall temperature gain and the amount of time taken for any one placement to reach a peak, but did not necessarily prevent the differentials from exceeding the 35 deg F limit, nor prevent cracking in any placement; and 5) Larger placements have a greater tendency to exceed the differential limit.

Low Modulus Hot Pour Joint Sealant for ACC Pavements, HR-534, 1990

Over the years, the Iowa Department of Transportation has established an outstanding network of connector highways across the state of Iowa. Construction and paving of these primary roadways has essentially been completed. Unfortunately, many of these primary highway pavements are reaching their design life and are in need of rehabilitation. The emphasis, therefore, has shifted from the construction of new highways to the maintenance and rehabilitation of existing highways. The Iowa DOT in recent years has become more concerned with preventing the ingress of surface water into the pavement structure. Crack sealing is receiving greater emphasis. Specifications have been modified to require improved low modulus crack and joint sealing materials.