This study is a continuation of a series dealing with the composition and properties of lightweight concrete developed 2000 years ago by the builders of an ancient culture, the Totonacas. The concrete was found in the main city of the Totonacas, "El Tajin", near the modern city of Veracruz in Mexico. The lightweight concrete was used to construct flat slabs in the pyramidal buildings which were found by accident by Mexican researchers. The paper presents a review of the developments leading to modern cements made by the Greek and Roman civilizations and compares these developments with the developments made independently in Mesoamerica. The properties of the concrete studied are: the mature of the interfacial zone, the microstructure and composition of the mortar phase and the aggregates used. Microstructure is characterized by the properties of a concrete of approximately the same age which was found in Camiros Greece.

In the Velenje Lignite Mine, Slovenia, the panel substructures are in sue. Fiber reinforced concrete panels are used because of their advantages which they have in the construction of mine railway lines over other types of substructures. In a development project, a fibre reinforced panel with much better carrying capacity and ductility in comparison with reinforced concrete panels has been developed. The panels, with high-performance fiber reinforced concrete (HP-FRC), which resist greater rock formation pressures have been developed also. These properties are input data for analysis of panel at the outside loading. Because the crack propagation in the length direction as well in the width direction is prevented by the presence of fibres in concrete, energy absorption capacity, toughness and ductility of concrete respectively are increased.

This paper give some results of flowing and high strength concretes using type F fly ash (FA) and naphthalene based superplasticizer (SP). In series S.Sp was used only to produce flowing concrete and in series H was used to reduce W/C and to cause the concrete to flow. In each studied series the portland cement content was maintained fixed of 250 kg/m3. Fly ash was added as a percentage of the normal portland cement from 10% up to 150%. For reference series a .8 W/C was used, and for series S. 200 liters of water was used to attain a nominal consistency of 60.0 cm DIN. For reference series H a reduction of 35% of mixing water of series S was used (70 L). To find the maximum amount of FA and SP dosage in series S, SP admixture was used to obtain the reference consistency of 60.0 cm DIN. In series H where the admixture was used as high-range water-reducing-retardant admixture (HRWRRA) in large dosages, the concrete becomes very cohesive and significant slump loss was noted. When superplasticizer-retardant admixture (SPRA) was used as HRWRRA to produce flowing concrete under established conditions, it was possible to obtain a very significant compressive strength gain at 56 days, which was the upper limit of the age covered in this study. An increment of 160% (from 25 to 65 Mpa) at 56 days was attained for series H in relation to the reference mixture without FA and SP. To obtain high strength concretes using high volumes of fly ash, it is essential to use SP admixture.

In this study three series of four test panels were molded varying the mortar content. In the three series, the dry-mix shooting process were regulated with three different conditions. In each test panel samples and cores were taken to determine shotcrete mix proportions and physical properties. The results show a good correlation between stiffness and W/C in according with the exponential model proposed by Powers, confirming the Proctor needle as a good instrument to dry-mix shotcrete workability control. The compaction and compressive strength were as high as the volume of paste incorporated in the shotcrete. This feature provides a typical dry rheological behavior to the fry-mix shotcrete, where the Abram's Law is not valid. It occurs regardless of the fine and coarse aggregates proportion, although the influence of which on rebound is very clear. It is recommended that one should not fix a maximum W/C for a given compressive strength in the dry-mix shotcrete specifications. On the contrary, the consistency measurement by the Proctor needle, appears to be a good instrument for dry-mix shotcrete workability control. The use of the aggregates gradation recommended by the Aci is a good way to achieve better shotcreting conditions with a minimum rebound.

Results of an experimental investigation on the performance of cracked fiber reinforced concrete in a simulated marine environment are presented. A total of 111 prismatic specimens (150 by 150 by 510 mm) comprising both lightweight and normal weight concretes were used in this investigation. Cracked specimens with crack sizes of "hairline", .25 mm, 1.0mm, and uncracked specimens were exposed in either simulated seawater for up to a period of 7 years or 5300 alternate wetting and drying cycles. It was found, for both lightweight and normal weight concrete, that the strength development of uncracked specimens is not hampered by alternate wetting and development of uncracked specimens is not hampered by alternate wetting and drying. At the end of 7 years exposure, compressive strength gain of 90% was observed over the seven day moist cured strength for both types of concrete. Corresponding uncracked prismatic specimens showed approximately 25% flexural strength gain; however their post-cracking strength decreased under a prolonged period of alternate wetting and drying. Precracked specimens with cracks of up to .25 mm showed improvement in load carrying capacity up to 1440 wetting and drying cycles. However specimens with cracks of 1.0 mm showed a reduction in load carrying capacity.