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The aim of this study is to investigate the effects of phosphogypsum on the properties of both cement pastes and mortars. Normal Portland cement CEM Ι 32,5N, Limestone Blended cement CEM ΙΙ B-L32,5N, and Slag cement CEM ΙΙ A-S32,5N were used. These cements were partially substituted by 0,2,4,6,8,10,and 15% of phosphogypsum. The test program was divided to two stages. In the first stage, tests were conducted according to BSEN 196, namely setting times (initial and final), soundness, and compressive strength (at ages 7 and 28 days). In the second stage, X-ray diffraction (XRD), and scanning electron microscope (SEM) were conducted on selected mixes from first stage. The results show that the three types of cements with the various replacement percentages of phosphogypsum met the limit of initial setting time, as well as, provided soundness of 2 mm. Also, in terms of compressive strength, it was proven, that it is possible to partially replace the three tested types of cements by phosphogypsum by up to 8%and 15% with regard to cement/sand ratio of (1:3) and (1:2) respectively.

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The aim of this study is to investigate the effects of incorporating dune sand as fine aggregates replacement in self-compacting concrete. Twelve mixes were cast and tested for both fresh and hardened properties. The mixes were divided into 2 groups: Each group comprised six mixes. The constituent materials were as follows: Normal Portland cement CEM Ι 42,5N, dolomite as coarse aggregates of maximum size 10 mm, medium-sized sand, silica fume was 10% by weight of cement. Coarse: fine aggregates ratio was 1:1. Admixture which complies with ASTM C494 Types G and F was used in the 12 mixes (3.5% by weight of cement ).Dune sand replaced natural sand by zero %,10%,25%,50%, 75%,and 100% respectively .For , the first group (Group A), the cement content was 350 Kg/m3, while for the second group (Group B), the cement content was 400 Kg/m3.Tests carried out on fresh self-compacting concrete were slump flow,T50cm ,V-funnel, V-funnel t5min ,and GTM screen stability test . Tests conducted on hardened concrete were compressive strength at ages 7 and 28 days, flexural, and splitting tensile strengths were also conducted at age 28 days. The obtained results showed that the fresh properties satisfied the Egyptian Technical Specification limits. Regarding the hardened properties, both 28 days compressive and flexural strengths exhibited improvement till 50% replacement when compared to their respective control mixes.

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