Air Content and Permeability of PCC Pavements: 1909 to 2006, MLR-05-02, 2007

Portland cement concrete pavements have given excellent service history for Iowa. Many of these pavements placed during the 1920’s and 1930’s are still in service today. Many factors go in to achieve a long term durable concrete pavement. Probably the most important is the durability of the aggregate. Until the 1930’s, pit run gravel was the most predominant aggregate used. Many of these gravels provided long term performance and their durability is dependent upon the carbonate fraction of the gravel. Later, limestone (calcium carbonate) and dolomite (calcium, magnesium carbonate) sources were mined across Iowa. The durability of these carbonate aggregates is largely dependent upon the pore system which can cause freeze thaw problems known as D-cracking, which was a problem with some sources during the 1960’s. Also, some of these carbonate aggregates are also susceptible to deterioration from deicing salts. Geologists have identified the major components that affect the durability of these carbonate aggregates and sources are tested to ensure long term performance in Portland cement concrete. Air entrainment was originally put in concrete to improve scaling resistance. It is well known that air entrainment is required to provide freeze thaw protection in concrete pavements today. In Iowa, air entrainment was not introduced in concrete pavements until 1952. This research investigates properties that made older concrete pavements durable without air entrainment.

Oeuvres de George Sand. 10

Collection : Bibliothèque choisie

Oeuvres de George Sand. 12

Collection : Bibliothèque choisie

César Cascabel / par Jules Verne ; 85 dessins de George Roux...

Collection : Collection Hetzel

Correspondance : 1812-1876. II. 1836-1847 / George Sand

Collection : Bibliothèque contemporaine

Correspondance : 1812-1876. V. 1864-1870 / George Sand

Collection : Bibliothèque contemporaine

Correspondance : 1812-1876. I. 1812-1836 / George Sand

Collection : Bibliothèque contemporaine

Correspondance : 1812-1876. IV. 1854-1863 / George Sand

Collection : Bibliothèque contemporaine

Correspondance : 1812-1876. VI. 1870-1876 / George Sand

Collection : Bibliothèque contemporaine

Correspondance : 1812-1876. III. 1848-1853 / George Sand

Collection : Bibliothèque contemporaine

Colonization by mites of glacier-free areas in King George Island, Antarctica

This work aimed to investigate the ratio of colonization by terrestrial mites on ice-free areas created by the ongoing climate-induced melting of Antarctic glaciers. Glacier retreat opens new ice-free areas for the colonization by vegetation and animals. The study was undertaken on the Antarctic Specially Protected Area no. 128 (West Coast of the Admiralty Bay, King George Island, South Shetlands Islands). Transects marked between the Ecology, Baranowski and Windy Glaciers, and a sea shore were used to collect soil samples. Oribatid mites were found only on near-shore areas, on patches of vegetation of more than 30 years of age. The colonization by mite communities is strongly determined by the presence of plants.