Life Times, Winter 2008-2009

The IPERB newsletter is published by the Public Employment Relations Board. The opinions expressed should not be considered official opinions of the Iowa PERB.

Life Times, Winter 2007-2008

The IPERB newsletter is published by the Public Employment Relations Board. The opinions expressed should not be considered official opinions of the Iowa PERB.

Life Times, Summer 2007

The IPERB newsletter is published by the Public Employment Relations Board. The opinions expressed should not be considered official opinions of the Iowa PERB.

Life Times, Winter 2006-2007

The IPERB newsletter is published by the Public Employment Relations Board. The opinions expressed should not be considered official opinions of the Iowa PERB.

Life Times, Summer 2006

The IPERB newsletter is published by the Public Employment Relations Board. The opinions expressed should not be considered official opinions of the Iowa PERB.

Sign of the Times, December 2012-January 2013

Newsletter produced by Deaf Services Commission of Iowa

Sign of the Times, November 2013 - February 2014

Newsletter produced by Deaf Services Commission of Iowa

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.

Sign of the Times, March-May 2014

Newsletter produced by Deaf Services Commission of Iowa

Sign of the Times, September-November 2014

Newsletter produced by Deaf Services Commission of Iowa

Sign of the Times, September-November 2013

Newsletter produced by Deaf Services Commission of Iowa

Sign of the Times, June-July 2013

Newsletter produced by Deaf Services Commission of Iowa

Sign of the Times, March-May 2013

Newsletter produced by Deaf Services Commission of Iowa

Comparison of Setting Time Measured Using Ultrasonic Wave Propagation with Saw-Cutting Times on Pavements, TR-675, 2015

At present, there is little fundamental guidance available to assist contractors in choosing when to schedule saw cuts on joints. To conduct pavement finishing and sawing activities effectively, however, contractors need to know when a concrete mixture is going to reach initial set, or when the sawing window will open. Previous research investigated the use of the ultrasonic pulse velocity (UPV) method to predict the saw-cutting window for early entry sawing. The results indicated that the method has the potential to provide effective guidance to contractors as to when to conduct early entry sawing. The aim of this project was to conduct similar work to observe the correlation between initial setting and conventional sawing time. Sixteen construction sites were visited in Minnesota and Missouri over a two-year period. At each site, initial set was determined using a p-wave propagation technique with a commercial device. Calorimetric data were collected using a commercial semi-adiabatic device at a majority of the sites. Concrete samples were collected in front of the paver and tested using both methods with equipment that was set up next to the pavement during paving. The data collected revealed that the UPV method looks promising for early entry and conventional sawing in the field, both early entry and conventional sawing times can be predicted for the range of mixtures tested.