A method of forming a cement composition. The method comprises adding to a hydraulic cementitious material a first strength-enhancing agent and a second strength-enhancing agent, wherein the content of total alkali (Na.sub.2O equivalent) in the hydraulic cementitious material is less than or equal to 0.7% by weight of the cementitious material. The first strength-enhancing agent includes a compound represented by structural formula (I): ##STR00001##
and
the second strength-enhancing agent is sodium sulfate, potassium sulfate, or a mixture thereof. The example values of the variables in structural formula (I) and the example amounts of the first and second strength-enhancing agents being added are defined herein.

An accelerator for mineral binder compositions, especially for mortars or concrete, including: aluminium sulfate, at least one pozzolane, optionally at least one defoamer, and water. The accelerator is particularly useful for shotcrete, in the field of free-forming construction, or for additive manufacturing.

An unfired, refractory molded body (1), especially a plate, especially for thermal insulation of molten metal and/or an ingot solidifying from molten metal, that includes a binding agent matrix (2) of a set binder and aggregate grains (3) of biogenic silicic acid, preferably of rice husk ash, which are incorporated into the binding agent matrix (2), wherein the binding agent matrix (2) consists of silica gel, as well as a process for its production and its usage.

An unfired, refractory molded body (1), especially a plate, especially for thermal insulation of molten metal and/or an ingot solidifying from molten metal, that includes a binding agent matrix (2) of a set binder and aggregate grains (3) of biogenic silicic acid, preferably of rice husk ash, which are incorporated into the binding agent matrix (2), wherein the binding agent matrix (2) consists of silica gel, as well as a process for its production and its usage.

A method of forming a cement composition. The method comprises adding to a hydraulic cementitious material a first strength-enhancing agent and a second strength-enhancing agent, wherein the content of total alkali (Na.sub.2O equivalent) in the hydraulic cementitious material is less than or equal to 0.7% by weight of the cementitious material. The first strength-enhancing agent includes a compound represented by structural formula (I):

##STR00001##

and
the second strength-enhancing agent is sodium sulfate, potassium sulfate, or a mixture thereof. The example values of the variables in structural formula (I) and the example amounts of the first and second strength-enhancing agents being added are defined herein.