INFLUENCE OF CURING CONDITIONS ON THE EARLY STRENGTH OF LOW TEMPERATURE BELITE CEMENTS

Abstract

Low temperature belite cements are produced using techniques that stabilize the more reactive high temperature polymorphs of dicalcium silicate (C2S) to improve early strength, but the effect of curing conditions on them is not well studied. The focus of this work is to assess the improvement of their early strength in different curing conditions. During the synthesis of the cements at 1000 ºC, the more reactive polymorphs, -C2S and ?-C2S, were stabilized using gypsum and hydrothermal treatment with potassium hydroxide. The phase composition of the synthesized cements was analysed using X-ray powder diffraction. The morphology and elemental composition of the C2S crystals and hydrated pastes was determined using a scanning electron microscope equipped with an energy-dispersive X-ray system. Mortar samples were cured in different conditions that include hot air and hot water curing at 60 ºC and 90 ºC. The 28-day strength development, capillary water porosity, water absorption, and ultrasonic pulse velocity were tested. The formation of hydration products and strength was dependent on the type of C2S polymorph. Curing at elevated temperatures improved the transport properties of mortars. Samples cured at 90 ºC in hot air obtained the highest early strength. The presence of -C2S and elevated curing temperatures significantly improve the early strength of the mortar samples. ABSTRAK:  Simen belite suhu rendah dihasilkan melalui teknik menstabilkan reaktif polimof dikalsium silikat (C2S) bersuhu tinggi bagi meningkatkan kekuatan awal, tetapi kesan keadaan pengawetan ke atasnya tidak dikaji dengan baik. Fokus kerja ini adalah bagi menilai peningkatan kekuatan awal pada keadaan pengawetan berbeza. Sintesis simen pada suhu 1000 ºC, iaitu pada polimof lebih reaktif, -C2S dan ?-C2S, telah distabilkan menggunakan rawatan gipsum dan hidroterma dengan kalium hidroksida. Fasa komposisi simen tersintesis dianalisa menggunakan pembelauan serbuk sinar-X. Komposisi morfologi dan unsur kristal C2S dan pes terhidrat ditentukan menggunakan pengimbas mikroskop elektron yang dilengkapi sistem sinar-X penyebar tenaga. Sampel mortar telah diawetkan dalam keadaan berbeza termasuk pengawetan udara panas dan air panas pada suhu 60 ºC dan 90 ºC. Perkembangan kekuatan keliangan kapilari air, penyerapan air, dan halaju nadi ultrasonik telah diuji pada hari ke 28. Pembentukan produk penghidratan dan kekuatan adalah bergantung kepada jenis polimof C2S. Pengawetan pada suhu tinggi meningkatkan sifat pengangkutan mortar. Sampel yang diawet pada 90 ºC dalam udara panas memperoleh kekuatan awal tertinggi. Kehadiran -C2S dan suhu pengawetan tinggi dengan ketara meningkatkan kekuatan awal sampel mortar.