The aim of the present study is to investigate the use of diatomite as a partial replacement for cement in the production of cement mortar. Diatomite was used at 0%, 5%, 10% and 15% replacement by weight for cement while sand and water quantities were kept constant. Compressive and flexural strength, freeze–thaw resistance, sulfate resistance, water absorption and dry unit weight of the mortars were determined. The compressive and flexural strength decreased with increasing diatomite content for all curing periods. However the compressive strength of the cement mortar which was produced with 5% diatomite content complied with the minimum specified value of given in the standards. Diatomite replacement generally increased the compressive strength of the cement mortar after 25 freezing and thawing cycles. Water absorption of the mortars decreased with the increase of diatomite content except the mortar containing of 15% diatomite. Dry unit weight of the cement mortar was lower than the control mortar because of high porosity of diatomite. The expansion of the cement mortar bars immersed in 5% sodium sulfate solution decreased with increasing diatomite content and generally the sulfate resistance of the mortars was higher than that of the control mortar.

Diatomite is a sedimentary rock primarily composed of the skeletons of microscopic single celled aquatic plants called diatoms. The skeletons are composed of amorphous silica (silicon dioxide, SiO2), a very durable substance. Besides its amorphous silica content diatomite rocks commonly contain carbonate and clay minerals, quartz and feldspars. Diatoms skeletons are highly porous, light in weight and chemically stable and inert [1].

Diatomite has been used in variety of applications, mainly as filtration agent and functional fillers for paints and plastics. Because of its resistant to heat and chemical action it is also used in fireproof cement, insulation materials as an absorbent in explosives manufacture [2] and [3].

Diatomite is used as pozzolanic additives for Portland cement and mortars and grouts. Aydin and Gul [4] studied the effect of diatomite as additive on the properties of concrete. They indicate that the increase of additive ratio results a sudden decrease in compressive strength. The pozzolanic reaction of diatomite leads to the formation of higher amounts of hydrate products, especially at the age of 28 days [5]. Stamatakis et al. [6] demonstrated that the use of diatomite rocks as cement additives has drawbacks such as higher water demand, but compressive strength of the laboratory produced cements exhibit higher values than that of the reference Portland cement. This diatomite rock had the greatest amount of silica content reflecting its high opal-A content. Fragoulis et al. [7] investigated that the addition of diatomite in cement results an increase of its specific surface (Blaine) because of their high grindability. The high specific surface was mainly due to the nature of the rock that was composed of very fine-grained particular such as diatom frustules, clay particles and calcareous grains. The combination of reactive silica and high Blaine results in cement with improved mechanical properties. According to Tonak [8] the main drawback of the diatomite addition to cement is the increase in water demand and fineness of produced cement. Diatomite rocks are very soft materials and grinding with clinker and gypsum has advantages in view of lower specific energy consumption. Aruntas [9] indicated that the addition of diatomite in cement has a great effect on its grain size increasing its fineness.

Due to its low thermal conductivity, diatomite could be used in bricks and other products for thermal and acoustical insulation. Unal et al. [10] studied the physical and mechanical properties of lightweight concrete produced with diatomite as lightweight aggregate. Test results indicated that lightweight concrete could be used in construction to obtain high isolation and reduce dead load of construction. Uygunoglu and Unal [11] also investigated the properties of lightweight block element produced with diatomite as divide element to reduce dead load of construction. Diatomite had been used by the ancient Greeks and Romans as an abrasive and making lightweight building bricks and stone [12].

The experimental research program outlined in this paper is designated to investigate the influence of diatomite on some properties of cement mortar, namely, compressive and flexural strength, water absorption, dry unit weight, freeze–thaw resistance and sulfate resistance.