Alkali-activated concrete mixes with ground granulated blast furnace slag and paper sludge ash in seawater environments

Pre­dicted sea level rise due to global warm­ing will ne­ces­si­tate the con­struc­tion of coastal de­fenses to pro­tect the pop­u­la­tions in the vicin­ity of the coasts. Large quan­ti­ties of con­crete will be re­quired with con­sec­u­tive in­creases in green­house emis­sions, hence an in­creas­ing need for al­ter­na­tive to Or­di­nary Port­land Ce­ment (OPC) ce­ments. Fea­si­ble po­ten­tial al­ter­na­tives could be found in al­kali-ac­ti­vated ce­ments , which also in­clude in­dus­trial by-prod­ucts or waste ma­te­ri­als. This pa­per pre­sents a lab­o­ra­tory study of con­crete mixes based on the al­kali-ac­ti­va­tion of an in­dus­trial by-prod­uct, ground gran­u­lated blast fur­nace slag (GG­BFS) and in­cludes an in­dus­trial waste, pa­per slugde ash (PSA) in the al­kali-ac­ti­va­tor mixes. The use of sea­wa­ter as mix­ing and cur­ing wa­ter was also ex­am­ined. The com­pres­sive strength and a num­ber of dura­bil­ity-re­lated prop­er­ties of al­kali-ac­ti­vated mixes in ma­rine en­vi­ron­ment were in­ves­ti­gated and com­pared to OPC sys­tems. The in­cor­po­ra­tion of pa­per sludge ash led to high early strengths, a de­crease in the ef­fec­tive poros­ity of al­kali-ac­ti­vated slag con­cretes and gen­er­ally a re­duced wa­ter ab­sorp­tion, and en­hanced the per­for­mance against chlo­ride ion at­tack in mixes with fresh­wa­ter, as well as the re­sis­tance of the ce­ments in sul­phate at­tack es­pe­cially when mixed with sea­wa­ter. The ad­di­tion of sea­wa­ter in the mixes in­creased the re­sis­tance to sul­phate at­tack and the com­pres­sive strength in al­kali-ac­ti­vated sys­tems, as op­posed to OPC con­cretes in which mix­ing and cur­ing in sea­wa­ter had dele­te­ri­ous ef­fects. The study gives promise for the suit­abil­ity of the tested al­kali-ac­ti­vated con­crete mixes in sea­wa­ter en­vi­ron­ments.