Concrete Materials Storage, Mixing and Delivery, November 2004

Proper storage practices are critical to protect materials from intermingling, contamination, or degradation, and to maintain consistent aggregate gradation throughout a project. Concrete Paving Workforce Reference no.1

Governor's Youth Race and Detention Task Force; Full Force, May 2009

This report, the Full Report, is the culmination of the Task Force’s responsibilities as set out in Executive Order 5, dated October 30, 2007. The Executive Order specifies a number of goals and report requirements.There is a commonly held perception that the use of detention may serve as a deterrent to future delinquency. Data in this report reflect that approximately 40% of youth detained in 2006 were re-detained in 2006. Research conducted by national experts indicates that, particularly for low risk/low level offenders, that the use of detention is not neutral, and may increase the likelihood of recidivism. Comparable data for Iowa are not available (national data studied for this report provide level of risk, but risk level related to detention is not presently available for Iowa). The Task Force finds no evidence suggesting that recidivism levels (as related to detention risk) in Iowa should be different than found in other states. Data in this report also suggest that detention is one of the juvenile justice system’s more costly sanctions ($257 - $340 per day). Other sites and local jurisdictions have been able to redirect savings from the reduced use of juvenile detention to support less costly, community-based detention alternatives without compromising public safety.

Improving Portland Cement Concrete Mix Consistency and Production Rate through Two-Stage Mixing, TR-505, 2007

A two-stage mixing process for concrete involves mixing a slurry of cementitious materials and water, then adding the slurry to coarse and fine aggregate to form concrete. Some research has indicated that this process might facilitate dispersion of cementitious materials and improve cement hydration, the characteristics of the interfacial transition zone (ITZ) between aggregate and paste, and concrete homogeneity. The goal of the study was to find optimal mixing procedures for production of a homogeneous and workable mixture and quality concrete using a two-stage mixing operation. The specific objectives of the study are as follows: (1) To achieve optimal mixing energy and time for a homogeneous cementitious material, (2) To characterize the homogeneity and flow property of the pastes, (3) To investigate effective methods for coating aggregate particles with cement slurry, (4) To study the effect of the two-stage mixing procedure on concrete properties, (5) To obtain the improved production rates. Parameters measured for Phase I included: heat of hydration, maturity, and rheology tests were performed on the fresh paste samples, and compressive strength, degree of hydration, and scanning electron microscope (SEM) imaging tests were conducted on the cured specimens. For Phases II and III tests included slump and air content on fresh concrete and compressive and tensile strengths, rapid air void analysis, and rapid chloride permeability on hardened concrete.