Hydrothermally-calcined waste paper ash nanomaterial as an alternative to cement for clay soil modification for building purposes

It has been observed that clay soil cannot be used for building design, unless it is modified by firing or with cement. Either method of stabilization can adversely affect the environment and public health just like indiscriminate dumping or open burning adopted in developing countries as the prevalent disposal technique for waste papers. This paper sought to examine the feasibility of using assorted waste papers to derive an alternative stabilizer to Portland Limestone Cement for modification of clay soil into composite materials suitable for building design. Specifically, clay-based composites were fabricated at 0 %, 5 %, 10 %, 15 %, and 20% replacement levels by weight with cement, and then hydrothermally-calcined waste paper ash nanomaterial (HCWPAN). Water absorption, sorptivity, bulk density, thermal conductivity, specific heat capacity, thermal diffusivity, flaking concentration, flexural strength, and compressive strength were investigated for each of the fabricated samples. Irrespective of the stabilizing agent utilized, 10% loading level was found to be the optimum for possession of maximum mechanical strength by the samples. Only samples with the HCWPAN content were found to be capable of reducing building dead loads and improving thermal insulation efficiency over un-stabilized clay material, if applied as walling elements in buildings. Generally, it was revealed that the cement and HCWPAN have comparable influences on the properties of clay soil, thus indicating that HCWPAN could be utilized as an alternative stabilizer to cement. In addition, the preparation of HCWPAN was found to be more energy-saving than that of the cement.

Performance of Concrete Pavement Incorporating Portland Limestone Cement in Cold Weather

The City of Winnipeg (COW) and the University of Manitoba (UM), Canada, have partnered since 2015 to conduct research on the use of portland limestone cement (PLC), comprising up to 15% limestone filler, in transportation infrastructure such as pavements and bridges. Laboratory tests have substantiated the equivalent or superior resistance of concrete made from PLC, relative to that made from general use (GU) cement (Type I) to durability exposures including acids, sulfate salts and chloride-based deicing salts. Subsequently, a field trial was done in 2018, which involved casting two concrete pavement sections made from PLC and GU cement in Winnipeg, Manitoba, Canada. The current paper reports on the construction and long-term (three years/winter seasons) properties of these pavement sections including fresh properties, strength, absorption and chloride ions penetrability, as well as microstructural features. Cores were taken from mid-slabs and at joints, which are the most vulnerable locations to damage in concrete pavements. The field trial results showed that concrete pavement sections made with PLC had equivalent or superior performance compared with those made of GU in terms of fresh, hardened and durability properties. Thus, it presents a viable option for sustainable construction of concrete flatwork in cold regions.

Prediction of Sulfate Attack Products in Portland-Limestone Cements: The Effect of Cation Type and Concentration

Portland-limestone cement materials are susceptible to sulfate attack at low temperature and high humidity, because such conditions facilitate the formation of thaumasite, detriment to the structural integrity of calcium silicate hydrates (C─S─H). In this work, the effect of the cation associated with sulfates, concentration of sulfate solution, and limestone content in cement, were thermodynamically simulated. MgSO4 solution is of higher risk, degrading extensively the structural integrity of C─S─H. Although this phase is partially preserved under the effect of Na2SO4 and K2SO4 solutions, extensive expansion and thaumasite formation occur. The sulfate content of the corrosive solution and the limestone content in cement are the factors mostly intensifying the attack caused by MgSO4 and Na2SO4/K2SO4 solutions, respectively.