Constructional aspects of some heated concrete floors for greenhouses

Abstract The paper gives particular attention to the constructional aspects of concrete floors in greenhouses. In 1979 preliminary research was started in IMAG into the cultivation of vegetable seedlings on several floor materials, namely on ordinary concrete, porous concrete and asphalt. Overhead watering was provided, and the heating system was in the soil below the floor. These experiments revealed two problems. Uneven water distribution caused uneven growth and the mass of soil around and the concrete above the heating tubes caused a long response time for warming up and cooling down the concrete surface. For strength and wear resistance the ordinary concrete turned out to be the only suitable material. In 1981 IMAG made further trials with floors where heating and (flooded) watering system were integrated in the floor. These floors were made of reinforced concrete cast in situ , of asbestos cement and of concrete tiles. The 100 mm thick concrete floor cast in situ , turned out to be the most suitable because of the loading capacity and the good drainage of water. A standard specification was prepared for this floor type. At the end of 1985, applications of concrete floors in greenhouse, extended to 150 ha in the Netherlands for the production of vegetable seedlings, pot plants and cut flowers in pots or mats. If this trend continues there will be about 600 ha by 1990. Further development of the concrete floor has the objectives of improving thermal behaviour and easier removal or restoration of a floor. For that purpose two types of floor are under trial. 1. (1) An insulated concrete floor cast in situ that contains less concrete per square meter. 2. (2) A concrete floor built from removable concrete elements combined with a system for air movement between the plants.